Methods and apparatus for patient positioning in magnetic resonance imaging

ABSTRACT

According to some aspects, a magnetic resonance imaging system capable of imaging a patient is provided. The magnetic resonance imaging system comprising at least one B 0  magnet to produce a magnetic field to contribute to a B 0  magnetic field for the magnetic resonance imaging system and a member configured to engage with a releasable securing mechanism of a radio frequency coil apparatus, the member attached to the magnetic resonance imaging system at a location so that, when the member is engaged with the releasable securing mechanism of the radio frequency coil apparatus, the radio frequency coil apparatus is secured to the magnetic resonance imaging system substantially within an imaging region of the magnetic resonance imaging system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 120 and is acontinuation (CON) of U.S. patent application Ser. No. 16/516,373 filedJul. 19, 2019 and titled “Methods and Apparatus for Patient Positioningin Magnetic Resonance Imaging,” which claims priority under 35 U.S.C. §119 to U.S. Provisional Application Ser. No. 62/700,711 filed Jul. 19,2018 and titled “Methods and Apparatus for Patient Positioning inMagnetic Resonance Imaging,” and U.S. Provisional Application Ser. No.62/811,361 filed Feb. 27, 2019 and titled “Methods and Apparatus forPatient Positioning in Magnetic Resonance Imaging,” each application ofwhich is herein incorporated by reference in its entirety.

BACKGROUND

Magnetic resonance imaging (MRI) provides an important imaging modalityfor numerous applications and is widely utilized in clinical andresearch settings to produce images of the inside of the human body. Asa generality, MRI is based on detecting magnetic resonance (MR) signals,which are electromagnetic waves emitted by atoms in response to statechanges resulting from applied electromagnetic fields. For example,nuclear magnetic resonance (NMR) techniques involve detecting MR signalsemitted from the nuclei of excited atoms upon the re-alignment orrelaxation of the nuclear spin of atoms in an object being imaged (e.g.,atoms in the tissue of the human body). Detected MR signals may beprocessed to produce images, which in the context of medicalapplications, allows for the investigation of internal structures and/orbiological processes within the body for diagnostic, therapeutic and/orresearch purposes.

MRI provides an attractive imaging modality for biological imaging dueto the ability to produce non-invasive images having relatively highresolution and contrast without the safety concerns of other modalities(e.g., without needing to expose the subject to ionizing radiation,e.g., x-rays, or introducing radioactive material to the body).Additionally, MRI is particularly well suited to provide soft tissuecontrast, which can be exploited to image subject matter that otherimaging modalities are incapable of satisfactorily imaging. Moreover, MRtechniques are capable of capturing information about structures and/orbiological processes that other modalities are incapable of acquiring.However, there are a number of drawbacks to MRI that, for a givenimaging application, may involve the relatively high cost of theequipment, limited availability and/or difficulty in gaining access toclinical MRI scanners and/or the length of the image acquisitionprocess.

The trend in clinical MRI has been to increase the field strength of MRIscanners to improve one or more of scan time, image resolution, andimage contrast, which, in turn, continues to drive up costs. The vastmajority of installed MRI scanners operate at 1.5 or 3 tesla (T), whichrefers to the field strength of the main magnetic field B₀. A rough costestimate for a clinical MRI scanner is approximately one million dollarsper tesla, which does not factor in the substantial operation, service,and maintenance costs involved in operating such MRI scanners.

Additionally, conventional high-field MRI systems typically requirelarge superconducting magnets and associated electronics to generate astrong uniform static magnetic field (B₀) in which an object (e.g., apatient) is imaged. The size of such systems is considerable with atypical MRI installment including multiple rooms for the magnet,electronics, thermal management system, and control console areas. Thesize and expense of MRI systems generally limits their usage tofacilities, such as hospitals and academic research centers, which havesufficient space and resources to purchase and maintain them. The highcost and substantial space requirements of high-field MRI systemsresults in limited availability of MRI scanners. As such, there arefrequently clinical situations in which an MRI scan would be beneficial,but due to one or more of the limitations discussed above, is notpractical or is impossible, as discussed in further detail below.

SUMMARY

Some embodiments include a patient handling apparatus configured tofacilitate positioning a patient within a magnetic resonance imagingdevice, the patient handling apparatus comprising a patient supporthaving a surface adapted to be positioned between the patient and a bedso that, when positioned, the surface of the patient support isunderneath at least a portion of the patient's body, and a securingportion comprising at least one first releasable securing mechanismconfigured to engage with a radio frequency component to secure theradio frequency component to the securing portion, and at least onesecond releasable securing mechanism configured to engage with themagnetic resonance imaging device to secure the securing portion to themagnetic resonance imaging device.

Some embodiment include a helmet configured to accommodate a patient'shead during magnetic resonance imaging, the helmet comprising at leastone radio frequency transmit and/or receive coil, and at least one firstreleasable securing mechanism configured to engage with a memberattached to a magnetic resonance imaging system at a location such that,when the at least one securing mechanism engages with the member, thehelmet is positioned within the imaging region of the magnetic resonanceimaging system.

Some embodiments include a helmet configured to accommodate a patient'shead during magnetic resonance imaging, the helmet comprising at leastone radio frequency transmit and/or receive coil, at least one firstreleasable securing mechanism configured to engage with a member of themagnetic resonance imaging system such that, when the at least onesecuring mechanism engages with the member, the at least one securingmechanism resists translation of the helmet relative to the cooperatingmember, and at least one second securing mechanism configured to, whenengaged with a cooperating portion of the member, prevent rotation ofthe helmet about the member.

Some embodiments include a magnetic resonance imaging system capable ofimaging a patient at least partially supported by a support comprisingferromagnetic material, the magnetic resonance imaging system comprisingat least one first B₀ magnet to produce a first magnetic field tocontribute to a B₀ magnetic field for the magnetic resonance imagingsystem, the B₀ magnetic field having a field strength of less than orequal to 0.2T, at least one second B₀ magnet to produce a secondmagnetic field to contribute to the B₀ magnetic field for the magneticresonance imaging system, wherein the at least one first B₀ magnet andthe at least one second B₀ magnet are arranged relative to one anotherso that an imaging region is provided there between, and a memberconfigured to engage with a releasable securing mechanism of a radiofrequency coil apparatus, the member attached to the magnetic resonanceimaging between the at least one first B₀ magnet and the at least onesecond B₀ magnet at a location so that, when the member is engaged withthe releasable securing mechanism of the radio frequency coil apparatus,the radio frequency coil apparatus is secured to the magnetic resonanceimaging system substantially within the imaging region.

Some embodiments include a magnetic resonance imaging system capable ofimaging a patient at least partially supported by a support comprisingferromagnetic material, the magnetic resonance imaging system comprisingat least one first B₀ magnet to produce a first magnetic field tocontribute to a B₀ magnetic field for the magnetic resonance imagingsystem, the B₀ magnetic field having a field strength of less than orequal to 0.2T, at least one second B₀ magnet to produce a secondmagnetic field to contribute to the B₀ magnetic field for the magneticresonance imaging system, wherein the at least one first B₀ magnet andthe at least one second B₀ magnet are arranged relative to one anotherso that an imaging region is provided there between, and a memberconfigured to engage with a releasable securing mechanism of a patienthandling apparatus configured to secure a radio frequency coilapparatus, the member attached to the magnetic resonance imaging betweenthe at least one first B₀ magnet and the at least one second B₀ magnetat a location so that, when the member is engaged with the releasablesecuring mechanism of the patient handling apparatus, the radiofrequency coil secured to the patient handling apparatus is positionedsubstantially within the imaging region.

Some embodiments include a method, comprising releasably securing asupport to a magnetic resonance imaging device so as to facilitatemagnetic resonance imaging of a patient, the support disposed betweenthe patient and a standard medical bed.

Some embodiments include a method comprising positioning a portion ofanatomy of a patient within an imaging region of a magnetic resonanceimaging system while the patient is at least partially supported by astandard medical bed, and acquiring at least one magnetic resonanceimage of the portion of the anatomy of the patient while the patient isat least partially supported by the standard medical bed.

Some embodiments include an apparatus for imaging a foot, the apparatuscomprising at least one housing configured to accommodate a patient'sfoot during magnetic resonance imaging, at least one radio frequencytransmit and/or receive coil, and at least one first releasable securingmechanism configured to engage with a member attached to a magneticresonance imaging system at a location such that, when the at least onesecuring mechanism engages with the member, the apparatus is positionedwithin the imaging region of the magnetic resonance imaging system.

Some embodiments include an apparatus for imaging a foot, the apparatuscomprising at least one radio frequency transmit and/or receive coil,and at least one housing configured to accommodate a patient's footduring magnetic resonance imaging, the at least one housing tilted at anangle relative to a vertical axis

Some embodiments include a bridge adapted for attachment to a magneticresonance imaging system and configured to facilitate positioning apatient within the magnetic resonance imaging system, the bridgecomprising a support having a surface configured to support at least aportion of the patient, the support being moveable between an upposition and a down position, wherein the surface is substantiallyvertical in the up position and substantially horizontal in the downposition, a hinge configured to allow the support to be moved from theup position to the down position and vice versa, and a base configuredto attach the bridge to the magnetic resonance imaging system.

Some embodiments include a magnetic resonance imaging system comprisinga B₀ magnet configured to generate a magnetic field suitable formagnetic resonance imaging, a conveyance mechanism configured to allowthe magnetic resonance imaging system to be moved to differentlocations, and a bridge configured to facilitate positioning a patientwithin the magnetic resonance imaging system, the bridge comprising asupport having a surface configured to support at least a portion of thepatient, the support being moveable between an up position and a downposition, wherein the surface is substantially vertical in the upposition and substantially horizontal in the down position, a hingeconfigured to allow the support to be moved from the up position to thedown position and vice versa, and a base attaching the bridge to themagnetic resonance imaging system.

Some embodiments include a method of imaging a portion of anatomy of apatient while the patient is at least partially supported by a standardmedical bed, the method comprising positioning a magnetic resonanceimaging system and the bed proximate one another, moving a bridgeattached to the magnetic resonance imaging system from a verticalposition to a horizontal position so that the bridge overlaps a portionof the bed, positioning the patient via the bridge so that the portionof anatomy of the patient is within an imaging region of the magneticresonance imaging system, and acquiring at least one magnetic resonanceimage of the portion of the anatomy of the patient while the patient isat least partially supported by the bed and at least partially supportedby the bridge.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects and embodiments of the disclosed technology will bedescribed with reference to the following figures. It should beappreciated that the figures are not necessarily drawn to scale.

FIG. 1 illustrates exemplary components of a magnetic resonance imagingsystem;

FIGS. 2A and 2B illustrate a portable low-field MRI system, inaccordance with some embodiments.

FIG. 3 illustrates a portable MRI system, in accordance with someembodiments;

FIGS. 4A-I illustrate a patient handling apparatus that facilitates MRIof a patient from a standard hospital bed, in accordance with someembodiments;

FIGS. 5A-F illustrate aspects of a securing portion of a patienthandling apparatus, in accordance with some embodiments;

FIGS. 6A-B illustrate a releasable securing mechanism, in accordancewith some embodiments;

FIGS. 7A-B illustrate aspects of a releasable securing mechanism of aradio frequency coil apparatus, in accordance with some embodiments.

FIGS. 8A-B illustrate aspects of a releasable securing mechanism of aradio frequency coil apparatus, in accordance with some embodiments;

FIGS. 9A-B illustrate a see-through radio frequency helmet, inaccordance with some embodiments;

FIG. 10-D illustrate view of a foot coil, in accordance with someembodiments;

FIG. 11 illustrates a foot coil configured to accommodate a wider foot,in accordance with some embodiments; and

FIGS. 12A-D illustrate a foot coil positioned within a magneticresonance imaging device, in accordance with some embodiments;

FIG. 13A illustrates a fold-up bridge shown in a vertical or upposition, in accordance with some embodiment;

FIG. 13B illustrates the fold-up bridge illustrated in FIG. 13A in ahorizontal or down position, in accordance with some embodiments.

FIG. 14 illustrates components of a fold-up bridge, in accordance withsome embodiments;

FIG. 15A illustrates a model of a bridge, in accordance with someembodiments;

FIG. 15B illustrates a stress plot of the model of the bridgeillustrated in FIG. 15A;

FIG. 15C illustrates a deflection plot of the model of the bridgeillustrated in FIG. 15A.

FIG. 15D is Figure A.19 from the IEC 60601-1 illustrating the human bodymass distribution for patient support surfaces;

FIGS. 16A and 16B illustrate components of a fold-up bridge with acounter-balance mechanism, in accordance with some embodiments;

FIG. 17A illustrates a portable MRI system with a bridge in the verticalposition;

FIG. 17B illustrates a portable MRI system with a bridge in thehorizontal position;

FIG. 17C illustrates a patient positioned within a portable MRI systemand supported by a fold-out bridge.

DETAILED DESCRIPTION

The MRI scanner market is overwhelmingly dominated by high-fieldsystems, and particularly for medical or clinical MRI applications. Asdiscussed above, the general trend in medical imaging has been toproduce MRI scanners with increasingly greater field strengths, with thevast majority of clinical MRI scanners operating at 1.5T or 3T, withhigher field strengths of 7T and 9T used in research settings. As usedherein, “high-field” refers generally to MRI systems presently in use ina clinical setting and, more particularly, to MRI systems operating witha main magnetic field (i.e., a B₀ field) at or above 1.5T, thoughclinical systems operating between 0.5T and 1.5T are often alsocharacterized as “high-field.” Field strengths between approximately0.2T and 0.5T have been characterized as “mid-field” and, as fieldstrengths in the high-field regime have continued to increase, fieldstrengths in the range between 0.5T and 1T have also been characterizedas mid-field. By contrast, “low-field” refers generally to MRI systemsoperating with a B₀ field of less than or equal to approximately 0.2T,though systems having a B₀ field of between 0.2T and approximately 0.3Thave sometimes been characterized as low-field as a consequence ofincreased field strengths at the high end of the high-field regime.Within the low-field regime, low-field MRI systems operating with a B₀field of less than 0.1T are referred to herein as “very low-field” andlow-field MRI systems operating with a B₀ field of less than 10 mT arereferred to herein as “ultra-low field.”

As discussed above, conventional MRI systems require specializedfacilities. An electromagnetically shielded room is required for the MRIsystem to operate and the floor of the room must be structurallyreinforced. Additional rooms must be provided for the high-powerelectronics and the scan technician's control area. Secure access to thesite must also be provided. In addition, a dedicated three-phaseelectrical connection must be installed to provide the power for theelectronics that, in turn, are cooled by a chilled water supply.Additional HVAC capacity typically must also be provided. These siterequirements are not only costly, but significantly limit the locationswhere MRI systems can be deployed. Conventional clinical MRI scannersalso require substantial expertise to both operate and maintain. Thesehighly trained technicians and service engineers add large on-goingoperational costs to operating an MRI system. Conventional MRI, as aresult, is frequently cost prohibitive and is severely limited inaccessibility, preventing MRI from being a widely available diagnostictool capable of delivering a wide range of clinical imaging solutionswherever and whenever needed. Typically, patient must visit one of alimited number of facilities at a time and place scheduled in advance,preventing MRI from being used in numerous medical applications forwhich it is uniquely efficacious in assisting with diagnosis, surgery,patient monitoring and the like.

As discussed above, high-field MRI systems require specially adaptedfacilities to accommodate the size, weight, power consumption andshielding requirements of these systems. For example, a 1.5T MRI systemtypically weighs between 4-10 tons and a 3T MRI system typically weighsbetween 8-20 tons. In addition, high-field MRI systems generally requiresignificant amounts of heavy and expensive shielding. Many mid-fieldscanners are even heavier, weighing between 10-20 tons due, in part, tothe use of very large permanent magnets and/or yokes. Commerciallyavailable low-field MRI systems (e.g., operating with a B₀ magneticfield of 0.2T) are also typically in the range of 10 tons or more due tothe large amounts of ferromagnetic material used to generate the B₀field, with additional tonnage in shielding. To accommodate this heavyequipment, rooms (which typically have a minimum size of 30-50 squaremeters) have to be built with reinforced flooring (e.g., concreteflooring), and must be specially shielded to prevent electromagneticradiation from interfering with operation of the MRI system. Thus,available clinical MRI systems are immobile and require the significantexpense of a large, dedicated space within a hospital or facility, andin addition to the considerable costs of preparing the space foroperation, require further additional on-going costs in expertise inoperating and maintaining the system.

In addition, currently available MRI systems typically consume largeamounts of power. For example, common 1.5T and 3T MRI systems typicallyconsume between 20-40 kW of power during operation, while available 0.5Tand 0.2T MRI systems commonly consume between 5-20 kW, each usingdedicated and specialized power sources. Unless otherwise specified,power consumption is referenced as average power consumed over aninterval of interest. For example, the 20-40 kW referred to aboveindicates the average power consumed by conventional MRI systems duringthe course of image acquisition, which may include relatively shortperiods of peak power consumption that significantly exceeds the averagepower consumption (e.g., when the gradient coils and/or RF coils arepulsed over relatively short periods of the pulse sequence). Intervalsof peak (or large) power consumption are typically addressed via powerstorage elements (e.g., capacitors) of the MRI system itself. Thus, theaverage power consumption is the more relevant number as it generallydetermines the type of power connection needed to operate the device. Asdiscussed above, available clinical MRI systems must have dedicatedpower sources, typically requiring a dedicated three-phase connection tothe grid to power the components of the MRI system. Additionalelectronics are then needed to convert the three-phase power intosingle-phase power utilized by the MRI system. The many physicalrequirements of deploying conventional clinical MRI systems creates asignificant problem of availability and severely restricts the clinicalapplications for which MRI can be utilized.

Accordingly, the many requirements of high-field MRI renderinstallations prohibitive in many situations, limiting their deploymentto large institutional hospitals or specialized facilities and generallyrestricting their use to tightly scheduled appointments, requiring thepatient to visit dedicated facilities at times scheduled in advance.Thus, the many restrictions on high field MRI prevent MRI from beingfully utilized as an imaging modality. Despite the drawbacks ofhigh-field MRI mentioned above, the appeal of the significant increasein SNR at higher fields continues to drive the industry to higher andhigher field strengths for use in clinical and medical MRI applications,further increasing the cost and complexity of MRI scanners, and furtherlimiting their availability and preventing their use as ageneral-purpose and/or generally-available imaging solution.

The low SNR of MR signals produced in the low-field regime (particularlyin the very low-field regime) has prevented the development of arelatively low cost, low power and/or portable MRI system. Conventional“low-field” MRI systems operate at the high end of what is typicallycharacterized as the low-field range (e.g., clinically availablelow-field systems have a floor of approximately 0.2T) to achieve usefulimages. Though somewhat less expensive than high-field MRI systems,conventional low-field MRI systems share many of the same drawbacks. Inparticular, conventional low-field MRI systems are large, fixed andimmobile installments, consume substantial power (requiring dedicatedthree-phase power hook-ups) and require specially shielded rooms andlarge dedicated spaces. The challenges of low-field MRI have preventedthe development of relatively low cost, low power and/or portable MRIsystems that can produce useful images.

The inventors have developed techniques enabling portable, low-field,low power and/or lower-cost MRI systems that can improve the wide-scaledeployability of MRI technology in a variety of environments beyond thecurrent MRI installments at hospitals and research facilities. As aresult, MRI can be deployed in emergency rooms, small clinics, doctor'soffices, in mobile units, in the field, etc. and may be brought to thepatient (e.g., bedside) to perform a wide variety of imaging proceduresand protocols. Some embodiments include very low-field MRI systems(e.g., 0.1T, 50 mT, 20 mT, etc.) that facilitate portable, low-cost,low-power MRI, significantly increasing the availability of MRI in aclinical setting.

There are numerous challenges to developing a clinical MRI system in thelow-field regime. As used herein, the term clinical MRI system refers toan MRI system that produces clinically useful images, which refers toimages having sufficient resolution and adequate acquisition times to beuseful to a physician or clinician for its intended purpose given aparticular imaging application. As such, the resolutions/acquisitiontimes of clinically useful images will depend on the purpose for whichthe images are being obtained.

Among the numerous challenges in obtaining clinically useful images inthe low-field regime is the relatively low SNR. Specifically, therelationship between SNR and B₀ field strength is approximately B₀^(5/4) at field strength above 0.2T and approximately B₀ ^(3/2) at fieldstrengths below 0.1T. As such, the SNR drops substantially withdecreases in field strength with even more significant drops in SNRexperienced at very low field strength. This substantial drop in SNRresulting from reducing the field strength is a significant factor thathas prevented development of clinical MRI systems in the very low-fieldregime. In particular, the challenge of the low SNR at very low fieldstrengths has prevented the development of a clinical MRI systemoperating in the very low-field regime. As a result, clinical MRIsystems that seek to operate at lower field strengths haveconventionally achieved field strengths of approximately the 0.2T rangeand above. These MRI systems are still large, heavy and costly,generally requiring fixed dedicated spaces (or shielded tents) anddedicated power sources.

The inventors have developed low-field and very low-field MRI systemscapable of producing clinically useful images, allowing for thedevelopment of portable, low cost and easy to use MRI systems notachievable using state of the art technology. According to someembodiments, an MRI system can be transported to the patient to providea wide variety of diagnostic, surgical, monitoring and/or therapeuticprocedures, generally, whenever and wherever needed. There arechallenges to providing an MRI system that can be transported to thepatient and/or operated outside specialized facilities (e.g., outsidesecure and shielded rooms), a number of which are addressed using thetechniques described in U.S. Pat. No. 10,222,434 (hereinafter, “the '434patent”), titled “Portable Magnetic Resonance Imaging Methods andApparatus,” issued Mar. 5, 2019, which patent is herein incorporated byreference in its entirety.

Another challenge involves positioning the patient within the MRI systemfor imaging. As discussed above, conventional MRI is confined tospecialized facilities, including a room for the device itself that isoutfitted with extensive shielding and must meet stringent safetyregulations, including requiring the room to be secure and free fromferrous material due to the high field strengths involved inconventional clinical MRI. Standard hospital beds are constructed usingferrous material, often steel, prohibiting there use with conventionalclinical MRI systems. As a result, a patient must be brought to thespecialized facility dedicated to the MRI system and transferred to acustom bed designed for use with the MRI system.

For patients that are ambulatory, this may mean requiring the patient toenter the secure room housing the MRI device and positioning themselveson a MRI-safe bed integrated with the MRI device. For patients that arenot ambulatory or are otherwise immobilized, the patient may need to befirst transferred to a customized MRI-safe bed to be transported to thesecure room and then transferred to the integrated bed of the MRIsystem. Such requirements limit the circumstances in which a patient canundergo MRI and in some cases prohibits the use of MRI entirely. Forexample, transfer of non-ambulatory and/or immobile patients to an MRIsafe bed or wheel chair to transport the patient into the secure roomand, potentially, another transfer to the integrated bed or patientsupport of the MRI system is difficult and, in some circumstances, notfeasible for medical safety reasons. Additionally, MRI safe beds arecostly and not widely available.

The inventors have developed techniques that allow MRI to be performedin conjunction with a standard patient support, such as a standardhospital bed or standard wheelchair, thereby eliminating the requirementof transferring patients one or more times, as well eliminating costsand availability issues associated with specialized MRI safe transports(e.g., beds, wheelchairs, etc.). Additionally, techniques that allow MRIto be performed, for example, from a standard hospital bed, facilitatepoint-of-care MRI. According to some embodiments, MRI is performed atfield strengths that are low enough to allow for imaging to be performedon a patient positioned on or in a standard patient support, forexample, a patient lying on a standard hospital bed or seated in astandard wheelchair. As used herein, a standard hospital bed or standardwheelchair refers to a patient support that has not been outfitted foruse with conventional high-field MRI. Standard hospital beds orwheelchairs will often be constructed of ferromagnetic material, such assteel, that prevents there use with high-field MRI.

To image a patient from, for example, a standard hospital bed, certainMRI imaging procedures may require positioning target anatomy of thepatient within an MRI system moved to a location, for example, the bedon which the patient is currently lying. The inventors have developedtechniques for facilitating the positioning of a patient within an MRIsystem for imaging of desired anatomy of the patient. According to someembodiments, a patient handling system that can be secured to the MRIsystem is used to support the patient and position the desired anatomyof the patient within the MRI system.

Conventional MRI systems typically include an integrated bed or supportfor the patient that is constructed using non-ferrous material tosatisfy stringent regulatory requirements (e.g., regulations promulgatedto ensure both patient and clinician safety) and so as to not disturbthe magnetic fields produced by the MRI system. This customized MRI-safebed is generally configured to be slid into and out of the bore of thesystem and typically has mounts that allow the appropriate radiofrequency coil apparatus to be connected over the portion of the anatomyto be imaged. When preparing a patient for imaging, the patient ispositioned on the bed outside the magnet bore so that the radiofrequency coil apparatus can be positioned and attached to thecooperating mounts on the bed. For example, for a brain scan, a radiofrequency head coil apparatus is positioned about the patient's head andattached to cooperating mounts fixed to the bed. After the radiofrequency coil apparatus is attached and positioned correctly, the bedis moved inside the B₀ magnet so that the portion of the anatomy beingimaged is positioned within the image region of the MRI system.

The inventors have recognized that this conventional process is notapplicable to portable or point-of-care MRI, nor can this process beused to image a patient from a standard medical bed or wheelchair. Forexample, standard medical beds are not equipped with mounts to which aradio frequency coil apparatus can be attached, nor are radio frequencycoil apparatus configured to be attached to standard medical beds. Inaddition, a standard medical bed or wheelchair cannot be positionedwithin the imaging region of an MRI system. To facilitate imaging from,for example, a standard medical bed, the inventors have developed radiofrequency coil apparatus adapted to accommodate target anatomy of apatient and configured to engage with a cooperating member attached tothe MRI system so that when the radio frequency coil apparatus isengaged with the member, the target anatomy is positioned within theimaging region of the MRI system. In this way, the radio frequency coilapparatus can be positioned about the patient and then attached to aportable MRI system so that the patient can be imaged from a standardmedical bed or wheelchair, allowing the MRI system to be brought to thepatient or the patient wheeled to an available MRI system and imagedfrom the standard medical bed. Such point-of-care MRI allows MRI to beutilized in a wide variety of medical situations where conventional MRIis not available (e.g., in the emergency room, intensive care unit,operating rooms, etc.).

According to some embodiments, a radio frequency helmet comprising oneor more radio frequency coils is adapted to accommodate a patient'shead. The radio frequency helmet comprises a releasable securingmechanism configured to secure the helmet to a member attached to theMRI system at a location so that whenever the radio frequency helmet issecured to the member, the helmet is substantially within the imagingregion of the MRI system. In particular, when the helmet accommodates apatient's head and is secured to the member, the patient's head ispositioned within the imaging region of the MRI system. According tosome embodiments, a radio frequency coil apparatus comprising one ormore radio frequency coils adapted to accommodate an appendage, such asa leg or an arm, is equipped with such a releasable securing mechanismso that when the radio frequency coil apparatus is secured to themember, the radio frequency coil apparatus is substantially within theimaging region of the MRI system so that the appendage positioned forimaging.

FIG. 1 is a block diagram of typical components of a MRI system 100. Inthe illustrative example of FIG. 1, MRI system 100 comprises computingdevice 104, controller 106, pulse sequences store 108, power managementsystem 110, and magnetics components 120. It should be appreciated thatsystem 100 is illustrative and that a MRI system may have one or moreother components of any suitable type in addition to or instead of thecomponents illustrated in FIG. 1. However, a MRI system will generallyinclude these high level components, though the implementation of thesecomponents for a particular MRI system may differ vastly, as discussedin further detail below.

As illustrated in FIG. 1, magnetics components 120 comprise B₀ magnet122, shim coils 124, RF transmit and receive coils 126, and gradientcoils 128. Magnet 122 may be used to generate the main magnetic fieldB₀. Magnet 122 may be any suitable type or combination of magneticscomponents that can generate a desired main magnetic B₀ field. Asdiscussed above, in the high field regime, the B₀ magnet is typicallyformed using superconducting material generally provided in a solenoidgeometry, requiring cryogenic cooling systems to keep the B₀ magnet in asuperconducting state. Thus, high-field B₀ magnets are expensive,complicated and consume large amounts of power (e.g., cryogenic coolingsystems require significant power to maintain the extremely lowtemperatures needed to keep the B₀ magnet in a superconducting state),require large dedicated spaces, and specialized, dedicated powerconnections (e.g., a dedicated three-phase power connection to the powergrid). Conventional low-field B₀ magnets (e.g., B₀ magnets operating at0.2T) are also often implemented using superconducting material andtherefore have these same general requirements. Other conventionallow-field B₀ magnets are implemented using permanent magnets, which toproduce the field strengths to which conventional low-field systems arelimited (e.g., between 0.2T and 0.3T due to the inability to acquireuseful images at lower field strengths), need to be very large magnetsweighing 5-20 tons. Thus, the B₀ magnet of conventional MRI systemsalone prevents both portability and affordability.

Gradient coils 128 may be arranged to provide gradient fields and, forexample, may be arranged to generate gradients in the B₀ field in threesubstantially orthogonal directions (X, Y, Z). Gradient coils 128 may beconfigured to encode emitted MR signals by systematically varying the B₀field (the B₀ field generated by magnet 122 and/or shim coils 124) toencode the spatial location of received MR signals as a function offrequency or phase. For example, gradient coils 128 may be configured tovary frequency or phase as a linear function of spatial location along aparticular direction, although more complex spatial encoding profilesmay also be provided by using nonlinear gradient coils. For example, afirst gradient coil may be configured to selectively vary the B₀ fieldin a first (X) direction to perform frequency encoding in thatdirection, a second gradient coil may be configured to selectively varythe B₀ field in a second (Y) direction substantially orthogonal to thefirst direction to perform phase encoding, and a third gradient coil maybe configured to selectively vary the B₀ field in a third (Z) directionsubstantially orthogonal to the first and second directions to enableslice selection for volumetric imaging applications. As discussed above,conventional gradient coils also consume significant power, typicallyoperated by large, expensive gradient power sources, as discussed infurther detail below.

MRI is performed by exciting and detecting emitted MR signals usingtransmit and receive coils, respectively (often referred to as radiofrequency (RF) coils). Transmit/receive coils may include separate coilsfor transmitting and receiving, multiple coils for transmitting and/orreceiving, or the same coils for transmitting and receiving. Thus, atransmit/receive component may include one or more coils fortransmitting, one or more coils for receiving and/or one or more coilsfor transmitting and receiving. Transmit/receive coils are also oftenreferred to as Tx/Rx or Tx/Rx coils to generically refer to the variousconfigurations for the transmit and receive magnetics component of anMRI system. These terms are used interchangeably herein. In FIG. 1, RFtransmit and receive coils 126 comprise one or more transmit coils thatmay be used to generate RF pulses to induce an oscillating magneticfield B₁. The transmit coil(s) may be configured to generate anysuitable types of RF pulses.

Power management system 110 includes electronics to provide operatingpower to one or more components of the low-field MRI system 100. Forexample, as discussed in more detail below, power management system 110may include one or more power supplies, gradient power components,transmit coil components, and/or any other suitable power electronicsneeded to provide suitable operating power to energize and operatecomponents of MRI system 100. As illustrated in FIG. 1, power managementsystem 110 comprises power supply 112, power component(s) 114,transmit/receive switch 116, and thermal management components 118(e.g., cryogenic cooling equipment for superconducting magnets). Powersupply 112 includes electronics to provide operating power to magneticcomponents 120 of the MRI system 100. For example, power supply 112 mayinclude electronics to provide operating power to one or more B₀ coils(e.g., B₀ magnet 122) to produce the main magnetic field for thelow-field MRI system. Transmit/receive switch 116 may be used to selectwhether RF transmit coils or RF receive coils are being operated.

Power component(s) 114 may include one or more RF receive (Rx)pre-amplifiers that amplify MR signals detected by one or more RFreceive coils (e.g., coils 126), one or more RF transmit (Tx) powercomponents configured to provide power to one or more RF transmit coils(e.g., coils 126), one or more gradient power components configured toprovide power to one or more gradient coils (e.g., gradient coils 128),and one or more shim power components configured to provide power to oneor more shim coils (e.g., shim coils 124).

In conventional MRI systems, the power components are large, expensiveand consume significant power. Typically, the power electronics occupy aroom separate from the MRI scanner itself. The power electronics notonly require substantial space, but are expensive complex devices thatconsume substantial power and require wall mounted racks to besupported. Thus, the power electronics of conventional MRI systems alsoprevent portability and affordability of MRI.

As illustrated in FIG. 1, MRI system 100 includes controller 106 (alsoreferred to as a console) having control electronics to sendinstructions to and receive information from power management system110. Controller 106 may be configured to implement one or more pulsesequences, which are used to determine the instructions sent to powermanagement system 110 to operate the magnetic components 120 in adesired sequence (e.g., parameters for operating the RF transmit andreceive coils 126, parameters for operating gradient coils 128, etc.).As illustrated in FIG. 1, controller 106 also interacts with computingdevice 104 programmed to process received MR data. For example,computing device 104 may process received MR data to generate one ormore MR images using any suitable image reconstruction process(es).Controller 106 may provide information about one or more pulse sequencesto computing device 104 for the processing of data by the computingdevice. For example, controller 106 may provide information about one ormore pulse sequences to computing device 104 and the computing devicemay perform an image reconstruction process based, at least in part, onthe provided information. In conventional MRI systems, computing device104 typically includes one or more high performance work-stationsconfigured to perform computationally expensive processing on MR datarelatively rapidly. Such computing devices are relatively expensiveequipment on their own.

As should be appreciated from the foregoing, currently availableclinical MRI systems (including high-field, mid-field and low-fieldsystems) are large, expensive, fixed installations requiring substantialdedicated and specially designed spaces, as well as dedicated powerconnections. As discussed above, the inventors have developed low power,portable low-field MRI systems that can be deployed in virtually anyenvironment and that can be brought to the patient who will undergo animaging procedure. In this way, patients in emergency rooms, intensivecare units, operating rooms and a host of other locations can benefitfrom MRI in circumstances where MRI is conventionally unavailable. Theexemplary portable MRI systems described below in connection with FIGS.2A, 2B and 3A are capable of being moved to locations at which MRI isneeded (e.g., emergency and operating rooms, primary care offices,neonatal units, intensive care units, specialty departments, hospitalrooms, recovery units, etc.), facilitating point-of-care MRI operable inproximity to standard hospital equipment such as hospital beds,wheelchairs, other medical devices, computing equipment, life supportsystems, etc. Additionally, the exemplary portable MRI systems describedherein, including the systems described in the '434 patent, allow forthe deployment of the MRI system in virtually any location so that apatient can be easily brought to the MRI system (e.g., transported usinga standard hospital bed or wheelchair) to achieve point-of-care MRI.

FIGS. 2A and 2B illustrate a low power, portable low-field MRI system,in accordance with some embodiments. Portable MRI system 200 comprises aB₀ magnet 205 including at least one first permanent magnet 210 a and atleast one second permanent magnet 210 b magnetically coupled to oneanother by a ferromagnetic yoke 220 configured to capture and channelmagnetic flux to increase the magnetic flux density within the imagingregion (field of view) of the MRI system. Permanent magnets 210 a and210 b may be constructed using any suitable technique, (e.g., using anyof the techniques, designs and/or materials described in the '434patent). Yoke 220 may also be constructed using any of the techniquesdescribed herein (e.g., using any of the techniques, designs and/ormaterials described in the '434 patent). It should be appreciated that,in some embodiments, B₀ magnet 205 may be formed using electromagnetsusing any of the electromagnet techniques described herein (e.g., usingany of the techniques, designs and/or materials described in the '434patent). B₀ magnet 205 may be encased or enclosed in a housing 212 alongwith one or more other magnetics components, such as the system'sgradient coils (e.g., x-gradient, y-gradient and z-gradient coils)and/or any shim components (e.g., shim coils or permanent magneticshims), B₀ correction coils, etc.

B₀ magnet 205 may be coupled to or otherwise attached or mounted to base250 by a positioning mechanism 290, such as a goniometric stage(examples of which are described in the '434 patent), so that the B₀magnet can be tilted (e.g., rotated about its center of mass) to providean incline to accommodate a patient's anatomy as needed. In FIG. 2A, theB₀ magnet is shown level without an incline and, in FIG. 2B, the B₀magnet is shown after undergoing a rotation to incline the surfacesupporting the patient's anatomy being scanned. Positioning mechanism290 may be fixed to one or more load bearing structures of base 250arranged to support the weight of B₀ magnet 205.

In addition to providing the load bearing structures for supporting theB₀ magnet, base 250 also includes an interior space configured to housethe electronics 270 needed to operate the portable MRI system 200. Forexample, base 250 may house the power components to operate the gradientcoils (e.g., X, Y and Z) and the RF transmit/receive coils. Theinventors have developed generally low power, low noise and low costgradient amplifiers configured to suitably power gradient coils in thelow-field regime, designed to be relatively low cost, and constructedfor mounting within the base of the portable MRI system (i.e., insteadof being statically racked in a separate room of a fixed installment asis conventionally done). Examples of suitable power components tooperate the gradient coils are described in further detail below (e.g.,the power components described in connection with FIGS. 20-34).According to some embodiments, the power electronics for powering thegradient coils of an MRI system consume less than 50 W when the systemis idle and between 100-300 W when the MRI system is operating (i.e.,during image acquisition). Base 250 may also house the RF coilamplifiers (i.e., power amplifiers to operate the transmit/receive coilsof the system), power supplies, console, power distribution unit andother electronics needed to operate the MRI system, further details ofwhich are described below.

According to some embodiments, the electronics 270 needed to operateportable MRI system 200 consume less than 1 kW of power, in someembodiments, less than 750 W of power and, in some embodiments, lessthan 500 W of power (e.g., MRI systems utilizing a permanent B₀ magnetsolution). Techniques for facilitating low power operation of an MRIdevice are discussed in further detail below. However, systems thatconsume greater power may also be utilized as well, as the aspects arenot limited in this respect. Exemplary portable MRI system 200illustrated in FIGS. 2A and 2B may be powered via a single powerconnection 275 configured to connect to a source of mains electricity,such as an outlet providing single-phase power (e.g., a standard orlarge appliance outlet). Accordingly, the portable MRI system can beplugged into a single available power outlet and operated therefrom,eliminating the need for a dedicated power source (e.g., eliminating theneed for a dedicated three-phase power source as well as eliminating theneed for further power conversion electronics to convert three phasepower to single phase power to be distributed to correspondingcomponents of the MRI system) and increasing the availability of the MRIsystem and the circumstances and locations in which the portable MRIsystem may be used.

Portable MRI system 200 illustrated in FIGS. 2A and 2B also comprises aconveyance mechanism 280 that allows the portable MRI system to betransported to different locations. The conveyance mechanism maycomprise one or more components configured to facilitate movement of theportable MRI system, for example, to a location at which MRI is needed.According to some embodiments, conveyance mechanism comprises a motor286 coupled to drive wheels 284. In this manner, conveyance mechanism280 provides motorized assistance in transporting MRI system 200 todesired locations. Conveyance mechanism 280 may also include a pluralityof castors 282 to assist with support and stability as well asfacilitating transport.

According to some embodiments, conveyance mechanism 280 includesmotorized assistance controlled using a controller (e.g., a joystick orother controller that can be manipulated by a person) to guide theportable MRI system during transportation to desired locations.According to some embodiments, the conveyance mechanism comprises powerassist means configured to detect when force is applied to the MRIsystem and to, in response, engage the conveyance mechanism to providemotorized assistance in the direction of the detected force. Forexample, rail 255 of base 250 illustrated in FIGS. 2A and 2B may beconfigured to detect when force is applied to the rail (e.g., bypersonnel pushing on the rail) and engage the conveyance mechanism toprovide motorized assistance to drive the wheels in the direction of theapplied force. As a result, a user can guide the portable MRI systemwith the assistance of the conveyance mechanism that responds to thedirection of force applied by the user. The power assist mechanism mayalso provide a safety mechanism for collisions. In particular, the forceof contact with another object (e.g., a wall, bed or other structure)may also be detected and the conveyance mechanism will react accordinglywith a motorized locomotion response away from the object. According tosome embodiments, motorized assistance may be eliminated and theportable MRI system may be transported by having personnel move thesystem to desired locations using manual force.

Portable MRI system 200 includes slides 260 that provide electromagneticshielding to the imaging region of the system. Slides 260 may betransparent or translucent to preserve the feeling of openness of theMRI system to assist patients who may experience claustrophobia duringconventional MRI performed within a closed bore. Slides 260 may also beperforated to allow air flow to increase the sense of openness and/or todissipate acoustic noise generated by the MRI system during operation.The slides may have shielding 265 incorporated therein to blockelectromagnetic noise from reaching the imaging region. According tosome embodiments, slides 260 may also be formed by a conductive meshproviding shielding 265 to the imaging region and promoting a sense ofopenness for the system. Thus, slides 260 may provide electromagneticshielding that is moveable to allow a patient to be positioned withinthe system, permitting adjustment by personnel once a patient ispositioned or during acquisition, and/or enabling a surgeon to gainaccess to the patient, etc. Thus, the moveable shielding facilitatesflexibility that allows the portable MRI system to not only be utilizedin unshielded rooms, but enables procedures to be performed that areotherwise unavailable. Exemplary slides providing varying levels ofelectromagnetic shielding are discussed in further detail below.

According to some embodiments, a portable MRI system does not includeslides, providing for a substantially open imaging region, facilitatingeasier placement of a patient within the system, reducing the feeling ofclaustrophobia and/or improving access to the patient positioned withinthe MRI system (e.g., allowing a physician or surgeon to access thepatient before, during or after an imaging procedure without having toremove the patient from the system). As an example, FIG. 3 illustratesan exemplary portable low-field magnetic resonance imaging system thatcan be moved to and operated at the point of care. MRI system 300 may besimilar to one or more of the portable MRI systems described in the '434patent, comprising a B₀ magnet 322 that includes at least one firstmagnet 322 a and at least one second magnet 322 b magnetically coupledto one another by a ferromagnetic yoke 320 configured to capture andchannel magnetic flux to increase the magnetic flux density within theimaging region (field of view) of the MRI system. Magnets 322 a and 322b may be constructed using any suitable technique, including any of thetechniques described in the '434 patent. For example, B₀ magnet 322 mayinclude permanent magnet(s), electromagnet(s), printed magnetics, or anythereof. MRI system 300 further comprises gradient coils 328 a and 328 bto provide X-gradient, Y-gradient and Z-gradient coils for spatialencoding of MR signals.

B₀ magnet 322 may be coupled to or otherwise attached or mounted to base350 to support the B₀ magnet. Base 350 includes housing 302 configuredto house the electronics needed to operate the portable MRI system 300(e.g., as described in detail in the '434 patent). To facilitatetransporting the system to the point of care, MRI system 300 may includea conveyance mechanism. In FIG. 3, wheels or castors 382 allow the MRIsystem to be wheeled to desired locations. According to someembodiments, MRI system 300 includes motorized assist to facilitatemaneuvering the system, some examples of which are described in the '434patent. For example, the conveyance mechanism may include a motor todrive wheels/castors 382 provide motorized assistance in transportingMRI system 300 to desired locations. According to some embodiments, theconveyance mechanism may include motorized assistance controlled using acontroller (e.g., a joystick or other controller that can be manipulatedby a person) to guide the portable MRI system during transportation todesired locations. According to some embodiments, the conveyancemechanism comprises power assist means configured to detect when forceis applied to the MRI system by an operator and to, in response, engagethe conveyance mechanism to provide motorized assistance in thedirection of the detected force, examples of which are described infurther detail in the '434 patent.

As shown, MRI system 300 may have a maximum horizontal width W thatfacilitates the maneuverability of the system within the facilities inwhich the MRI system is used. According to some embodiments, the maximumhorizontal dimension of a portable MRI system is in a range between 40and 60 inches and, more preferably, in a range between 35 and 45 inches.For example, exemplary MRI system 300 has a maximum horizontal width ofapproximately 40 inches. As a result, MRI system 300 can be brought tolocations in which the MRI is needed, including to the bedside of apatient to be imaged. MRI system 300 also includes bridge 373 that ismounted to the MRI system to facilitate positioning a patient within theimaging region of the MRI system. Bridge 373 may be configured to beattached to different locations around the base to allow a patient to bepositioned within the imaging region from different directions and/ororientations. According to some embodiments, bridge 373 is attached tothe MRI system 300 so that it can be moved around the perimeter of theB₀ magnet. According to some embodiments, bridge 373 is configured to beremoved and reattached at different locations around the perimeter ofthe B₀ magnet. According to some embodiments, the bridge may beconfigured to attach to yoke 320, base 350 or any other suitable portionof MRI system 300, as the aspects are not limited in this respect.

The exemplary low-field MRI systems discussed above and in the '434patent can be used to provide point-of-care MRI, either by bringing theMRI system directly to the patient or bringing the patient to arelatively nearby MRI system (e.g., by wheeling the patient to the MRIsystem in a standard hospital bed, wheelchair, etc.). To facilitateimaging of patients using the exemplary systems discussed herein, theinventors have developed techniques to allow a patient to be positionedsuch that the target anatomy is located correctly within the imagingregion of the MRI system, including techniques that allow the patient tobe positioned from a standard medical bed, wheelchair or other patientsupport, even when the patient has limited or no mobility (e.g., thepatient is unconscious, sedated or anesthetized, or otherwise haslimited autonomous motion).

Following below are more detailed descriptions of various conceptsrelated to, and embodiments of, allowing for point-of-care MRI using aportable low-field MRI. It should be appreciated that the embodimentsdescribed herein may be implemented in any of numerous ways. Examples ofspecific implementations are provided below for illustrative purposesonly. It should be appreciated that the embodiments and thefeatures/capabilities provided may be used individually, all together,or in any combination of two or more, as aspects of the technologydescribed herein are not limited in this respect.

FIG. 4A illustrates a patient handling apparatus that facilitatesperforming MRI on a patient from a standard hospital bed. FIG. 4A showsa first step of positioning target anatomy of patient 499 within imagingregion 415 of MRI system 400 (successive steps are illustrated in FIGS.4B-4I discussed in further detail below). In particular, a patient 499for which MRI is desired may be confined to a bed 490 for convenience,comfort or stabilization and/or because the patient is unconscious,immobilized or otherwise is not ambulatory or cannot be safely moved.Bed 490 may be a standard medical or hospital bed of the type typicallyused in emergency rooms, operating rooms, intensive care units, etc.Such standard hospital beds are typically constructed usingferromagnetic, often steel, that prohibits there use with conventionalclinical MRI systems. In addition, hospital beds often have motorizedcomponents for raising and lowering different portions of the bed thatalso often contain material not permitted to be located near aconventional clinical MRI system.

As used herein, the term standard hospital or medical bed refersgenerally to any bed that has not been manufactured to be MRI-safeaccording to regulations for current high-field MRI and/or that has notbeen customized for use with conventional high-field clinical MRIsystems (e.g., manufactured to be free of any ferromagnetic material).Therefore, standard medical or hospital bed includes not only generalpurpose hospital beds, but also beds that have been configured forspecific medical purposes other than customized beds manufactured to becompliant with current regulatory requirements for use with conventionalhigh field MRI. Thus, beds that are constructed of ferrous or ferritematerial (e.g., ferromagnetic material such as iron, steel, etc.) orother material prohibited from being used in restricted areas ofconventional clinical MRI are considered standard hospital beds, eventhough they may be customized for specific purposes.

For conventional clinical MRI, exemplary bed 490 may comprise a steelframe 495 so that, in addition to needing to be transported to adedicated MRI facility, the patient would be need to be transferred toan integrated bed of the MRI system and/or transferred to an MRI safebed (e.g., a specially made bed using aluminum or other non-magneticmaterial), or both. Such requirements limit the circumstances in which apatient can undergo MRI and in some cases prohibits the use of MRIentirely. In FIG. 4, low-field MRI system 400 has been transportedbed-side to the patient to perform point-of-care MRI. Alternatively,low-field MRI system 400 may be a local installation deployed in anemergency room, operating room, intensive care unit, doctor's office,etc. and bed 490 can be wheeled to the MRI system (i.e., MRI system 400need not be portable). Because of the low-field strengths of MRI system400, bed 490 can be safely brought into close proximity to B₀ magnet 422of MRI system 400. Additionally, low-field MRI techniques are morerobust to perturbations that may be caused by ferromagnetic materials ofthe bed or in the environment of the MRI system, allowing MRI system 400to be operated adjacent bed 490 and proximate other equipment in thevicinity that may include ferromagnetic material.

In the embodiment illustrated in FIG. 4A, patient handling apparatus 440is provided to assist in moving patient 499 into position within imagingregion 435 of MRI system 400. The imaging region or field of viewdefines the volume in which the B₀ magnetic field produced by the B₀magnet (e.g., B₀ magnet 422 comprising upper B₀ magnet 422 a, lower B₀magnet 422 b and yoke 420 illustrated in FIG. 4A) is suitable forimaging. More particularly, the imaging region or field of viewcorresponds to the region for which the B₀ magnetic field issufficiently homogeneous at a desired field strength that detectable MRsignals are emitted by an object positioned therein in response toapplication of radio frequency excitation (e.g., a suitable radiofrequency pulse sequence). In exemplary MRI system 400, B₀ magnet 422comprises an upper B₀ magnet 422 a and a lower B₀ magnet 422 b, eachproducing a magnetic field to contribute to the B₀ magnetic fieldproduced by B₀ magnet 422. Upper B₀ magnet 422 a and a lower magnet 422b are arranged in a bi-planar arrangement to form imaging region 435between them. B₀ magnet 422 also comprises yoke 420 to direct magneticflux from upper B₀ magnet 422 a and lower B₀ magnet 422 b to imagingregion 415 to increase the magnetic flux density therein.

Patient handling apparatus 440 comprises a support portion 442configured to support at least a portion of the patient while thepatient is positioned for imaging and a securing portion 445 configuredto releasably secure the patient handling apparatus to a radio frequencycoil apparatus (e.g., a radio frequency helmet) and to releasably securethe patient handling apparatus to MRI system 400, some embodiments ofwhich are described in further detail below. Securing portion 445includes at least one releasable securing mechanism configured to securethe patient handling apparatus to a member 429 attached to the MRIsystem. In the embodiment illustrated in FIG. 4A, member 429 is attachedto lower B₀ magnet 422 b of B₀ magnet 422 at a location so that when thepatient handling apparatus 440 is secured to member 429, the patienthandling apparatus is positioned between upper B₀ magnet 422 a and lowerB₀ magnet 422 b of the B₀ magnet. When a member to which a securingmechanism is configured to engage with is described as being attached toB₀ magnet 422 b, it means the member is attached to the cover or housingof the B₀ magnet, any structure contained within the cover or housingfor the B₀ magnet and/or attached to the B₀ magnet itself.

As discussed in further detail below, securing portion 445 may alsoinclude at least one releasable securing mechanism to secure patienthandling apparatus 440 to a radio frequency coil apparatus such thatwhen the patient handling apparatus 440 is secured to the radiofrequency coil apparatus and to member 429, the radio frequency coilapparatus is positioned at least partially in and, more preferably,substantially within the imaging region of MRI system 400. As a result,when target anatomy of a patient is positioned within the radiofrequency coil secured to the patient handling apparatus 400, and thepatient handling apparatus 400 is secured to member 429, the targetanatomy is positioned within imaging region 415 of MRI system 400 forimage acquisition.

As discussed above, patient handling apparatus comprises a supportportion 442 configured to support at least a portion of the patient'sbody to facilitate positioning the patient within the imaging region ofthe MRI system. Support portion 442 may include a fold or hinge 442 athat allows patient handling apparatus to be folded to make the patienthandling apparatus more compact, for example, during storage and/ortransport and unfolded, for example, during use. Support portion 442 maybe constructed from a molded plastic, such as polyethylene orpolypropylene. Fold 442 a may be a living hinge, a piano hinge, or anyother suitable hinge that facilitates the folding of support portion442. It should be appreciated that support portion 442 may includemultiple folds to increase compactness, or may not include a fold atall, as the aspects are not limited in this respect.

As shown in FIG. 4A, a bridge 473 may be mounted to MRI system 400 tofacilitate positioning patient handling apparatus 400 within MRI system400 to secure the securing portion 445 to member 429 via the at leastone releasable securing mechanism. According to some embodiments, bridge473 is configured to mount to bed 490 instead of MRI system 400.According to some embodiments, bridge 472 may be configured to bemountable to either the bed, the MRI system, or both, as the aspects arenot limited in this respect. Bridge 473 may be made of material thatreduces friction between patient handling apparatus 400 and the bridge,such as a smooth plastic, to facilitate sliding the patient support 440across the bridge so that securing portion 445 can be secured to member429 via the at least one releasable securing mechanism. Examples ofreleasable securing mechanisms for securing and releasing a patienthandling apparatus to and from a radio frequency coil apparatus and tosecure the patient handling apparatus to the MRI system, in accordancewith some embodiments, are described in further detail below.

FIG. 5A illustrates a securing portion of a patient handling apparatus,in accordance with some embodiments. Securing portion 545 may be similaror the same as securing portion 445 of patient handling apparatus 440illustrated in FIG. 4. In FIG. 5A, the bottom surface (underside) ofsecuring portion 545 is shown (i.e., the surface opposite the surface onwhich the patient is supported). That is, when the patient handlingapparatus to which securing portion 545 is coupled is positioned foruse, surface 545 a will face down towards the bed in the direction ofthe floor. In FIG. 5A, securing portion 545 is engaged with member 429of a magnetic resonance imaging system and a member 531 of a radiofrequency coil apparatus to illustrate techniques for securing a patienthandling apparatus to the radio frequency coil apparatus and magneticresonance imaging system to facilitate positioning a patient within themagnetic resonance imaging system, in accordance with some embodiments.

Securing portion 545 comprises a first releasable securing mechanism 543configured to engage with a radio frequency coil apparatus to secure thesecuring portion 545 (and thus the patient handling apparatus) to theradio frequency coil apparatus. In the exemplary embodiment illustratedin FIG. 5A, the first releasable securing mechanism 543 comprises aretention member 543 a and a keyhole slot 543 b to engage with member531 of a radio frequency coil apparatus (e.g., a radio frequency helmet)to secure the patient handling apparatus to the radio frequency coilapparatus. Keyhole slot 543 b includes a larger diameter portion 543 b′and a smaller diameter portion 543 b″ dimensioned so that member 531 canbe inserted into larger diameter portion 543 b′ in a first directionalong axis 505 c (i.e., in a direction out of the page of the drawing)and slid into smaller diameter portion 543 b″ where the smaller diameterprevents member 531 from exiting keyhole slot 543 b in a seconddirection along axis 505 c (i.e., in a direction opposite the directionmember 531 was inserted into keyhole slot 543 b). Securing portion 545may include additional keyhole slots 549 a and 549 b, each withrespective larger and smaller diameter portions (e.g., larger diameterportions 549 a′ and 549 b′, and smaller diameter portions 549 a″ and 549b″, respectively. Additional keyhole slots may be included to assist insecuring the radio frequency coil apparatus to the securing portion, anexample of which is illustrated in FIGS. 5B and 5C.

Retention member 543 a is configured to allow member 531 to be movedinto smaller diameter portion 543 b″ (i.e., in a first direction alongaxis 505 a) and to snap into place to retain member 531 in smallerdiameter portion 543 b″ (i.e., retention member 543 a resists movementof member 531 in a second direction along axis 505 a out of the smallerdiameter portion into the larger diameter portion). Accordingly, oncemember 531 has been moved from larger diameter portion 543 b′ to smallerdiameter portion 543 b″, smaller diameter portion 543 b″ and retentionmember 543 a secure the radio frequency coil apparatus to the securingportion 545. To disengage the radio frequency coil apparatus fromsecuring portion 545 of a patient handling apparatus, a force may beapplied against retention mechanism 543 a so that retention mechanism543 a moves aside to allow member 531 to be moved into larger diameterportion 543 b of keyhole slot 543 b so that the radio frequency coilapparatus can be lifted away from securing portion 545. For example, aforce applied to the radio frequency coil apparatus in the seconddirection along axis 505 a causes retention mechanism 543 b to slip sothat member 531 is allowed to slide into the larger diameter portion ofthe keyhole.

This process of securing a patient handling apparatus to, and releasingit from, a radio frequency helmet, is described in further detail belowin connection with FIGS. 5B and 5C. In particular, FIGS. 5B and 5Cillustrate the underside of a patient handling apparatus 540 comprisinga support portion 542 and securing portion 545 as it is engaging withradio frequency helmet 530. Radio frequency helmet 530 is configured toaccommodate the head of a patient and comprises one or more radiofrequency coils configured to transmit magnetic resonance pulsesequences and/or detect MR signals emitted from the patient in responseto a transmitted pulse sequence. The radio frequency coils may be, forexample, any of the radio frequency coils and geometries thereofdescribed in U.S. application Ser. No. 15/152,951, filed on May 31, 2016and titled “Radio Frequency Coil Methods and Apparatus.” Radio frequencyhelmet 530 comprise member 53 configured to engage with securingmechanism 543 of securing portion 545 of patient handling apparatus 540,and members 533 a and 533 b configured to engage with keyhole slots 549a and 549 b.

In FIG. 5B, members 531, 533 a and 533 b have been inserted intorespective keyhole slots 543 b, 549 a and 549 b and, more particularly,have been inserted through the respective larger diameter portions ofthe respective keyhole slots that are dimensioned to allow therespective member to be inserted into the respective keyhole slot. Bymoving the radio frequency coil apparatus 530 in the direction indicatedby arrow 505 (or moving the patient handling apparatus in the oppositedirection), members 531, 533 a and 533 b can be moved from the largerdiameter portion to the smaller diameter portion of the respectivekeyhole slot. For example, member 531 can be moved from larger diameterportion 543 b′ (see FIG. 5C) to the smaller diameter portion 543 b″ (seeFIG. 5B) of keyhole slot 543 b. The result of this movement isillustrated in FIG. 5C.

As shown in FIG. 5C, radio frequency helmet 530 has been secured topatient handling apparatus 540. Because the smaller diameter portions ofthe keyhole slots are dimensioned to be smaller than the diameter of theportion of the member inserted through the larger diameter portion ofthe keyhole slot, radio frequency helmet 530 cannot be lifted from thesecuring portion 545 of patient handling apparatus 540 without firstbeing returned to the large diameter portions. As also shown in FIG. 5c, retention member 543 snaps into place to resist movement of the member531 back into the larger diameter portion 543 b′ of keyhole slot 543 b.That is, retention member resists movement of radio frequency coilapparatus 530 in the direction indicated by arrow 505′. However, theresistance of retention member 543 a can be overcome by providing astrong enough force in the direction of arrow 505′ to return the radiofrequency coil apparatus 530 to the position illustrated in FIG. 5B sothat the radio frequency helmet 530 can moved away from or lifted off ofsecuring portion 545, thereby disengaging radio frequency helmet 530from patient handling apparatus 540. In this manner, securing mechanism543 releasably secures radio frequency helmet 530 to patient handlingapparatus 540 (e.g., by providing sufficient force to overcome theresistance of the retention member, the secured helmet can be releasedfrom the releasable securing mechanism 543).

FIGS. 6A and 6B illustrates a cross-sectional view of a radio frequencycoil apparatus 630 secured within a keyhole slot of a releasablesecuring mechanism of a securing portion 645 of a patient handlingapparatus. Radio frequency coil apparatus 630 comprises a member 631configured to engage with a keyhole slot of securing portion 645. Member631 comprises portions 631 a, 631 b and 631 c dimensioned differently sothat member 631 can be inserted into the keyhole slot and slid into asecured position. Foot portion 631 a is dimensioned to be sufficientlysmall so that it can be inserted into the larger diameter portion (notvisible in FIGS. 6A and 6B, but see e.g., larger diameter portion 543 b′illustrated in FIGS. 5A and 5C) of the keyhole slot and sufficientlylarge so it cannot be inserted into or removed from the smaller diameterportion 643 b″ of the keyhole slot (see also smaller diameter portion543 b″ illustrated in FIGS. 5A and 5B).

Neck portion 631 b is dimensioned to be sufficiently small so that itcan be accommodated by the smaller diameter portion 643 b″ of thekeyhole slot so that, after foot portion 631 a is inserted in the largerportion of the keyhole slot, member 631 can be moved into the smallerdiameter portion 643 b″. Body portion 631 c is dimensioned to besufficiently large so that it cannot be accommodated by either thesmaller or the larger diameter portions of the keyhole slot. Neckportion 631 b has height (e.g., its dimension in the direction of arrow605 c) so that when body portion 631 c prevents further insertion ofmember 631 into the keyhole slot (i.e, further movement in the directionof arrow 605 c is prevented by body portion 631 c), foot portion 631 ahas been positioned through the large diameter portion of the keyholeslot so that member 631 can be slid into the smaller diameter portion643 b″ to the secured position illustrated in FIGS. 6A and 6B. Becausefoot portion 631 a is larger than the smaller diameter portion 643 b″,member 631 cannot be lifted from securing portion 645 in the directionof arrow 605 c′ without first being transitioned back into the largerdiameter portion of the keyhole slot.

Referring again to FIG. 5A, according to some embodiments, retentionmember 543 a is made from plastic and is formed into a flat serpentinegeometry. For example, retention member 543 a may be a flat plasticspring, having a fixed end 543 a′ and a free end 543 a″ that can move toallow member 531 to be slid into smaller diameter portion 543 b″ andreturn to position to resist movement of member 531 back into largerdiameter portion 543 b′. The free end 543 a″ may be located in window503. The depth of window 503 (i.e., generally corresponding to thethickness of securing portion 545 in the direction along axis 505 c) maybe relatively small. As a result, retention member 543 a may also have arelatively small thickness in directions along axis 505 c (i.e., thethickness of the material forming the retention member, for example, thethickness of the plastic may be required to be relatively thin). Thatis, retention member 543 a may be constructed to be flat so that themember does not extend beyond surface 545 a (or extend beyond the topsurface of securing portion 545 on which the radio frequency apparatusrests when engaged). According to some embodiments, retention membercomprises a flat plastic spring with a thickness less than or equal toapproximately 0.5 inches. According to some embodiments, retentionmember comprises a flat plastic spring with a thickness less than orequal to approximately 0.25 inches. In this way, the retention mechanismcan be contained within the thickness of the securing portion 545.

Securing portion 545 may further comprise a second releasable securingmechanism 547 configured to engage with a magnetic resonance imagingsystem to secure the securing portion 545 (and thus the patient handlingapparatus) to the magnetic resonance imaging system. According to someembodiments, second releasable securing mechanism 547 comprises taperedlead-in portions 547 a that allows a member 429 attached to the magneticresonance imaging system to enter receptacle portion 547 e, andcomprises retention portions 547 b that prevent member 429 from exitingreceptacle 547 d. Pulls 547 d allow a user to retention portions 547 bto allow member 549 to exit receptacle 547 d. Springs 547 c allow thereleasable securing mechanism to be actuated, either by utilizing pulls547 d or under the force of member 429 pushing against tapered lead-inportions 547 a. It should be appreciated that the underside of member429 is illustrated in FIG. 5A to show how releasable securing mechanism547 engages with member 429, but that surface 429′ of member 429 is thesurface that is attached to the magnetic resonance imaging system, forexample, attached to lower B₀ magnet 422 b as shown in FIG. 4A.

FIGS. 5D-F illustrate the operation of an exemplary releasable securingmechanism 547. FIG. 5D illustrates releasable securing mechanism 547 ina closed position in which springs 547 c are in repose and taperedportions 547 a and retentions portion 547 b extend into receptacle 547e. Releasable securing mechanism 547 can be opened by applying a forceon pulls 547 d in the directions shown by arrows 505 b and 505 b′ or byapplying a force to tapered portions 547 a in the direction shown byarrows 505 a to move securing mechanism 547 to the open position shownin FIG. 5E. When releasable securing mechanism 547 is opened, springs547 c are compressed and tapered portions 547 a and retention portions547 b separate to allow entry and/or exit of member 439 into receptacle547 e. When the force applied to open securing mechanism 547 is removed,springs 547 c return to their repose position, forcing tapered portions547 a and retention portions 547 b towards each other to close the pathfor 439 into and out of receptacle 547 e, returning the releasablesecuring mechanism 547 to the position illustrated in FIG. 5D.

Force in the direction shown by arrows 505 a may be applied by pushingthe tapered portions 547 a against member 429, thereby compressingsprings 547 c and opening the securing mechanism to allow member 429 toenter receptacle 547 e. After member 429 enters receptacle 547 e,springs 547C return to their repose position and retention portions 547b close behind member 429 to secure securing portion 545 of patienthandling apparatus 540 to the magnetic resonance imaging system, asillustrated in FIG. 5F. As shown in FIG. 5F, member 429 may include asmaller diameter portion 429 a dimensioned to fit within receptacle 547e, and a larger diameter portion 429 b dimensioned to be larger thanreceptacle 547 e. Securing portion 545 is dimensioned so that at leastthe portions forming receptacle 547 e fit underneath larger diameterportion 429 b so that when securing portion 545 is engaged with member429 as shown FIG. 5F, the larger diameter portion 429 b prevents patienthandling apparatus 540 from being lifted away from the magneticresonance imaging system, while retention portions 547 b retain member429 within receptacle 547 e of releasable securing mechanism 547. Inparticular, for exemplary member 429 illustrated in FIG. 5F, the smallerdiameter portion 429 a has a height that allows those portions ofsecuring portion 545 forming receptacle 547 e to fit underneath largerdiameter portion 429 b to hold securing portion 545 to the surface towhich member 429 is attached.

To release patient handling apparatus from the magnetic resonanceimaging system, a user can apply a force to pulls 547 d in thedirections shown by arrows 505 b and 505 b′ to open releasable securingmechanism 547 (e.g., to place releasable securing mechanism 547 in theopen position illustrated in FIG. 5E). With the path out of receptacle547 e for member 429 opened, patient handling apparatus 540 can bedisengaged from the magnetic resonance imaging system. According to someembodiments, pulls 547 d are configured to operate independently of oneanother so that both sides need to be pulled to open securing mechanism547 d. According to some embodiments, pulling on either of pulls 547 dengages both sides so that only one pull needs to be used to opensecuring mechanism 547.

Referring again to FIG. 4A, member 429 may be attached to MRI system 400at a location such that when releasable securing mechanism 547 engagesmember 429 (e.g., as shown in FIGS. 5A and 5F), a radio frequency coilapparatus that has been secured to the patient handling apparatus islocated substantially within the imaging region of the MRI system. Forexample, when radio frequency helmet 530 is secured to securing portion545 of patient handling apparatus 540 via releasable securing mechanism543 and second releasable securing mechanism 547 is engaged with member429, radio frequency helmet 530 is positioned substantially within theimaging region of the MRI system (e.g., as shown in FIG. 4I). As aresult, when target anatomy is positioned within the radio frequencycoil apparatus, the target anatomy is within imaging region 415 of MRIsystem 400.

FIGS. 4A-4I illustrate exemplary steps that allow a patient to be imagedfrom a standard hospital bed, in accordance with some embodiments. InFIG. 4A, a patient handling apparatus 440 may be positioned on bed 490proximate patient 499 patient to begin the process of positioning thepatient within MRI system 400. As shown in FIG. 4B, patient 499 may berolled to the side or partially lifted so that patient handlingapparatus can be moved towards the center of bed 490 and/or generallyaligned with MRI system 400. Patient 499 can then be rolled back orreleased so that patient handling apparatus 440 is positioned betweenbed 490 and patient 499 and at least a portion of patient 499 issupported by support 442 of patient handling apparatus 440, as shown inFIG. 4C. The head of patient 499 may be positioned generally oversecuring portion 445 of patient handling apparatus 440, which itself maybe positioned proximate bridge 473 to facilitate positioning patient 499within MRI system 400.

As shown in FIG. 4D, a radio frequency helmet 430 may be positioned onbridge 473 or otherwise positioned to engage with securing portion 445of patient handling apparatus 440. Radio frequency helmet 430 may thenbe secured to securing portion 435 of patient handling apparatus 440with the patient's head positioned within the radio frequency helmet430, as shown in FIG. 4E. For example, radio frequency helmet 430 may besecured by engaging a releasable securing mechanism of securing portion435 with a cooperating member or members of radio frequency helmet 430,as discussed in connection with FIGS. 5A-C and FIGS. 6A-B. Patienthandling apparatus 440, with radio frequency helmet 430 secured, isready to be moved over bridge 473 to engage with member 429 to securethe patient handling apparatus to MRI system 400, as shown in FIG. 4F.

FIG. 4G illustrates patient handling apparatus 440 as the entrance to areleasable securing mechanism of securing portion 445 approaches member429 (e.g., approaches the entrance to a receptacle of the releasablesecuring mechanism). As shown, radio frequency helmet 430, which isaccommodating or holding the patient's head, has entered imaging region415 of MRI system 400. At the stage illustrated in FIG. 4H, member 429engages with tapered lead-in portions of a releasable securing mechanism(e.g., tapered lead-in portions 547 a of releasable securing mechanism547 illustrated in FIGS. 5A and 5D-F) causing the releasable securingmechanism to open to allow member 429 to enter a receptacle of thereleasable securing mechanism (e.g., receptacle 547 e illustrated inFIGS. 5A-F). Once member 429 has passed into the receptacle beyond thetapered lead-in portions, the releasable securing mechanism closes andretention portions of releasable securing mechanism prevent member 439from exiting the receptacle, as shown in FIG. 4I. In this position,patient handling apparatus 440 is secured to MRI system 400 and radiofrequency helmet 430 and the patient's head are positioned correctlywith imaging region 415 so that one or more image acquisition processesmay be performed.

As shown in FIGS. 4A-4I, point-of-care MRI may be performed by bringinga portable low field MRI system (e.g., MRI system 400) to the patient(or wheeling a patient to the MRI system in the patient's bed) so thatMRI can be performed on the patient from the patient's bed, even undercircumstances where the patient has limited or no mobility (e.g., thepatient is injured, unconscious or otherwise has limited mobility). As aresult, MRI may be made available in numerous circumstances where it waspreviously unavailable. As discussed above, because of the relativelylow field strengths involved in low-field MRI, MRI can be performed onthe patient without needing to transfer the patient to an MRI-safe bed,allowing for imaging of the patient from whatever bed the patient ispositioned on, opening up MRI to emergency rooms, operating rooms,intensive care units, doctor's offices and clinics, etc.

According to some embodiments, a radio frequency coil apparatus may beconfigured to be directly secured to an MRI system without first beingsecured to a patient handling apparatus. FIG. 7A illustrates a radiofrequency helmet configured to engage directly with the MRI system tosecure the radio frequency helmet within the imaging region of the MRIsystem to position the patient for imaging, in accordance with someembodiments. In particular, FIG. 7A illustrates the underside of a radiofrequency helmet 730 equipped with a releasable securing mechanism 735configured to engage with and grip a member 729 attached to the MRIsystem. Member 729 may be similar or the same as member 429 in that itis attached to the MRI system at a location such that when radiofrequency helmet 730 is secured to member 729, the radio frequencyhelmet 730 is positioned within the imaging region of the MRI system.Member 729 may also include a smaller diameter portion 729 a and alarger diameter portion 729 b configured to cooperate with releasablesecuring mechanism 735 to secure radio frequency helmet 730, asdiscussed in further detail below.

Releasable securing mechanism 735 comprises a receptacle dimensioned toaccommodate member 729 and a retention portion 737 configured to resistmovement of the cooperating member 729 once the member has beenpositioned within the receptacle, as shown in FIG. 7A. Exemplaryretention portion 737 comprises two arm portions 737 a and 737 b forminga portion of the receptacle and configured to grip member 729 whenmember 729 is positioned within the receptacle. According to someembodiments, arm portions 737 a and 737 b include protrusions 733 a and733 b, respectively, configured to resist movement of member 729 afterit has been inserted into the receptacle of releasable securingmechanism 735. Protrusions 733 a and 733 b comprise respective outwardfacing sides 733 a′ and 733 b′ and respective inward facing sides 733 a″and 733 b″ dimensioned to facilitate engaging with member 729 to secureradio frequency helmet 730 to the MRI system. According to someembodiments, the angle of the outward facing sides of protrusions 733 aand 733 b and the angle of the inward facing sides of protrusions areconfigured such that less forced is required to allow member 729 toenter into the receptacle of securing mechanism 735 than to allow member729 to exit from the receptacle. For example, the relative angles of theoutward and inward facing sides may be selected so that a relativelysmall force on the outward facing sides is needed to part arm portions737 a and 737 b to allow member 729 to enter the receptacle ofreleasable securing mechanism 735 and a larger force on the inwardfacing sides is needed to part arm portion 737 a and 737 b to allowmember 729 to be released from the receptacle of securing mechanism 735.It should be appreciated that protrusions 733 a and 733 b may bedimensioned in any way to achieve desired forces needed to engage anddisengage member 729 with securing mechanism 735, as the aspects are notlimited in this respect. Thus, radio frequency helmet 730 can be securedto and released from member 729 by applying a force in the appropriatedirection. That is, securing mechanism 735 is releasable because afterarm portions 737 a and 737 b grip member 729, the grip can be releasedby providing sufficient force on helmet 730 so that member 729 parts thearm portions 737 a and 737 b and releases the member.

As discussed above, the view in FIG. 7A is of the underside of the radiofrequency helmet 730 and member 729 so that surface 729′ is visible.However, this surface is attached to the MRI system at a location sothat when radio frequency helmet 730 is engaged with the member, thehelmet and target anatomy of the patient are positioned with the imagingregion of the MRI system (e.g., as shown in FIGS. 4A-4I). FIG. 7Billustrates a top view of releasable securing mechanism 735 engaged withmember 729 of an MRI system. As shown, arm portions 737 a and 737 b fitunderneath larger diameter portion 729 b and protrusions 733 a and 733 bgrip smaller diameter portion 729 a. In this manner, larger diameterportion 729 b prevents radio frequency helmet 730 from being lifted awayfrom member 729. That is, larger diameter portion 729 b restrictsmovement of radio frequency helmet 730 in the direction indicated byarrow 705 a. In addition, arms 737 a and 737 b restrict movement ofradio frequency helmet 730 in the directions illustrated by arrows 705 band 705 c (securing mechanism 735 restricts movement of member 727 inthe plane of the top surface 729″ of member 729). While the resistanceto movement of radio frequency helmet 730 out of securing mechanism 735can be overcome by applying sufficient force to the helmet as discussedabove, absent such a force, translational movement of radio frequencyhelmet 730 is generally prevented in all directions. However, releasablesecuring mechanism 735 may be configured to allow radio frequency helmetto be rotated about member 729 (e.g., about the axis along arrow 705 a).By allowing radio frequency helmet 730 this degree of freedom, radiofrequency coil can be oriented as desired about the center of the MRIsystem, providing flexibility as to the directions in which the patientcan be inserted into the MRI system. According to some embodiments, anadditional securing mechanism is provided to prevent rotation after adesired orientation has been reached, as discussed in further detail inconnection with FIGS. 8A and 8B.

FIGS. 8A and 8B illustrate an example of a releasable securing mechanismthat allows for rotation of the radio frequency coil apparatus about asecuring member of the MRI system to provide the above discussedflexibility, and that comprises an additional securing mechanism to holdthe radio frequency coil apparatus in place once a desired orientationhas been reached, in accordance with some embodiments. FIG. 8Aillustrates a cross-sectional view of a radio frequency helmet 830comprising a releasable securing mechanism 835 configured to engagemember 829 to secure the radio frequency helmet 830 to an MRI system.Releasable securing mechanism 835 may be similar to releasable securingmechanism 735 illustrated in FIGS. 7A and 7B. In particular, releasablesecuring mechanism 835 may include arm portions 837 a and 837 b (shownin FIG. 8B) configured to grip member 829 to resist translationalmovement of radio frequency helmet 830, but allow for rotation aboutmember 829. In addition, a second securing mechanism 831 is provided tohold radio frequency helmet 830 at a particular orientation about themember 829. For example, securing mechanism 831 may be a peg, pin orpost configured to cooperate with at least one recess 829 c (e.g., aslot, notch or other recess) provided in larger diameter portion 829 bof member 829. When radio frequency helmet 830 engages with member 829,the helmet can be rotated until the securing mechanism 831 finds recess829 c to hold the helmet at the fixed orientation of the recess. In thismanner, helmet 830 can be secured to member 829 and quickly rotated andheld in place at a corresponding desired orientation. It should beappreciated that member 829 may be provided with as many recesses aroundits perimeter as desired to allow a radio frequency helmet to be securedto an MRI system at the different corresponding orientations.

FIGS. 9A and 9B illustrate a see-through radio frequency helmet 930 toassist medical personnel in properly positioning a patient within helmet930. According to some embodiments, helmet 930 comprises an outerhousing 930 a and a coil support 930 b for transmit and/or receivecoils, both made of see-through material. The term see-through refers tostructure or material that is transparent or semitransparent (e.g.,translucent) so that the location of a patient's head can be viewedthrough the helmet. That is, see-through material refers to materialthat is sufficiently transparent to allow medical personnel to visuallyassess whether a patient is positioned correctly by looking through thehelmet. Coil support 930 b may be adapted to accommodate a patient'shead and provide a surface to which the transmit and/or receive coilsare disposed. Exemplary coil support 930 b provides a surface fortransmit coil(s) 990 a and receive coils 990 b. It should be appreciatedthat any configuration or geometry of transmit and/or receive coils maybe used, as the aspects are not limited in this respect.

Exemplary housing 930 a may contain electronics 970 that are used in theoperation of transmit/receive coils 930 a and 930 b, though suchelectronic may be positioned outside the housing, as the aspects are notlimited in this respect. Housing 930 a may be attached to base 950comprising a releasable securing mechanism 935 according to any one ormore of the techniques described herein to releasably secure helmet 930to a magnetic resonance imaging system within the imaging region of thesystem. FIG. 9B illustrates a radio frequency helmet 930 with a patient999 positioned within coil support 930 b. Because outer housing 930 aand coil support 930 b are see-through (e.g., constructed from atransparent or semitransparent plastic material), the patient's head canbe viewed through helmet 930, thus facilitating proper positioning ofpatient 999 within helmet 930. It should be appreciated that whileexemplary helmet 930 comprises a housing and a coil support, this is nota requirement. For example, according to some embodiments, a radiofrequency helmet may consist of a single surface on whichtransmit/receive coils are provided, and this surface may be made fromsee-through material to assist medical personnel in positioning apatient properly within the helmet.

As discussed above, techniques for providing a releasable securingmechanism may also be applied to a radio frequency coil apparatuscomprising one or more radio frequency coils adapted to accommodate anappendage, such as a leg or an arm, or a portion of an appendage such asan ankle, foot, wrist, hand, etc. FIGS. 10A-D illustrate aspects of afoot coil adapted to accommodate a foot and configured to secure thefoot coil to an MRI system so that the foot is positioned within theimaging region of the MRI system (e.g., within the imaging region of theexemplary low-field MRI systems described in the foregoing). Accordingto some embodiments, a radio frequency apparatus is adapted toaccommodate a foot and configured to be secured within the imagingregion of an MRI system having a bi-planar B₀ magnet configuration inwhich the space between upper and lower B₀ magnets may be limited, someexamples of which are described in further detail below.

FIG. 10A illustrates a view of a radio frequency apparatus 1030(referred to generally herein as a “foot coil,” adapted to accommodate afoot for one or more MRI procedures. Foot coil 1030 comprisestransmit/receive housings or supports 1030 t/r on or within whichtransmit and/or receive coils for the radio frequency apparatus areprovided. According to some embodiments, foot coil 1030 comprises atransmit housing for transmit coils and a receive housing for receivecoils, examples of which are illustrated in FIGS. 10B and 10C,respectively, discussed in further detail below. According to someembodiments, the transmit and receive coils may be provided on or withinthe same housing (e.g., transmit coils and receive coils may be providedon the same side of a shared housing, on outer and inner sides of thesame housing and/or one or more coils may be used for both transmit andreceive), as the aspects are not limited in this respect.

Exemplary foot coil 1030 also comprises an outer housing 1030 a to atleast partially cover transmit/receive housing(s) 1030 t/r and to form avolume 1030 c adapted to accommodate a foot. As illustrated in FIG. 10A,volume 1030 c has a height h and a w that allows a foot to be insertedinto the interior of foot coil 1030. In the embodiment illustrated inFIG. 10A, foot coil 1030 is constructed at an angle θ relative to thevertical axis. The inventors have recognized that angling the foot coilrelative to the vertical axis (e.g., generally pointing the toes awayfrom the vertical axis) may provide a number of advantages over avertical orientation. For example, a foot coil set at an angle relativeto the vertical (i.e., with a podal axis greater than zero degrees)facilitates accommodating larger feet within the imaging region of theMRI system. In particular, the distance between the upper and lower B₀magnets in the bi-planar configuration described in the foregoing placesa limit on the height h of the foot coil (e.g., the distance D labeledin FIG. 4G constrains the height of the foot coil that can beaccommodated by the MRI system). As shown in FIG. 10A, axis 1039 istilted from vertical by an angle θ. Axis 1039, referred to herein as thepodal axis, is the principal axis of the foot coil that is aligned withthe foot when inserted into volume 1030 c and the angle θ defines theangle of the podal axis away from the vertical axis 1025 in thedirection of the longitudinal axis 1041. That is, the podal axis refersto the axis that is aligned in the direction from the bottom of the footcoil where the heel of the foot is positioned towards the toes of thefoot when placed within the foot coil. A podal axis at zero degrees fromthe vertical axis 1025 in the direction of the longitudinal axis 1041(i.e., θ=0°) is aligned with the vertical axis in this respect, and apodal axis of 90 degrees from the vertical axis 1025 in the direction ofthe longitudinal axis 1041 (i.e., θ=90°) is aligned with thelongitudinal axis in this respect. Exemplary foot coil 1030 has a podalaxis 1039 of approximately 45 degrees from the vertical axis in thedirection of the longitudinal axis.

By angling the foot coil (i.e., tilting the podal axis away from thevertical axis), a longer foot can be accommodated within the imagingregion of, for example, the exemplary MRI systems described herein(e.g., MRI systems having the bi-planar configuration shown in FIGS.2-4). That is, the length of a foot that can be accommodated by the footcoil is greater than the height of the foot coil in the verticaldirection (i.e., L>h as shown in FIG. 10A). The more that foot coil 1030is angled relative to the vertical axis, the longer the foot that can beaccommodated within the same vertical height (i.e., the greater thelength L is relative to the height h). Because the human foot tends torest with the toes pointed away from the vertical axis (i.e., ratherthan having the toes straight above the heal), a foot coil thatgenerally mimics the natural repose of the foot may improve patientcomfort during an imaging procedure. Specifically, the angled or tiltedfoot coil may obviate the need for the patient to orient and hold theirfoot straight up and down, which may cause discomfort or pain,particularly in circumstances where the foot is injured from disease,infection or trauma. Though large angles (e.g., angles between 60 and 75degrees) may compromise the comfort of the patient in certaincircumstances, such angles may be used to construct a foot coil capableof accommodating longer feet.

To accommodate even larger feet, the foot coil may additionally betilted away from the vertical axis in a direction towards thelatitudinal axis. That is, the podal axis may be tilted by an angle φaway from the vertical axis 1025 in the direction of latitudinal axis1043 illustrated in FIG. 10A. The different tilt angles (i.e., tiltangles θ and φ) may be used alone or in combination to accommodate awide variety of foot sizes. A podal axis at zero degrees from thevertical axis 1025 in the direction of the latitudinal axis 1043 (i.e.,φ=0°) is aligned with the vertical axis in this respect, and a podalaxis of 90 degrees from the vertical axis 1025 in the direction of thelatitudinal axis 1043 (i.e., φ=90°) is aligned with the latitudinal axisin this respect.

It should be appreciated that the podal axis may be chosen as desired tosuit the needs of the imaging application and/or the patient andmultiple foot coils may be manufactured with different podal axes anddimensions to facilitate MRI of a wide variety of feet under differingcircumstances and conditions. According to some embodiments, the footcoil is tilted relative to vertical in the direction of the longitudinalaxis at an angle between 5 degrees and 60 degrees (i.e., a podal axiswith an angle θ between 5 and 60 degrees), more preferably between 15degrees and 50 degrees and, more preferably between 30 and 45 degrees(e.g., as illustrated by podal axis 1039 for exemplary foot coil 1030illustrated in FIG. 10A). According to some embodiments, the foot coilis tilted relative to vertical in the direction of the latitudinal axisat an angle between 5 degrees and 60 degrees (i.e., a podal axis with anangle φ between 5 and 60 degrees), more preferably between 15 degreesand 50 degrees and, more preferably between 30 and 45 degrees, or at anangle of approximately zero degrees as illustrated in FIG. 10A. Itshould be appreciated that a foot coil may be tilted to have a θcomponent, a φ component, or both. As discussed above, it should beappreciated that different foot coils may be constructed at differentangles to accommodate a wide variety of feet under a wide variety ofdifferent conditions and circumstances, and the exemplary podal axis anddimensions described herein are not limiting.

Foot coil 1030 also comprises back portion 1030 b that houses theelectronics for the foot coil when connected with bottom portion 1030b′. For example, the electronics forming portions of the radio frequencysignal chain (e.g., the transmit/receive circuitry) for operating thetransmit and receive coils may be housed in back portion 1030 b, 1030b′, as discussed in further detail below. Bottom portion 1030 b′ furthercomprises a terminal connection for cable bundle 1076 which carriespower, control and/or data (e.g., MR signal data) from the MRI system tothe transmit/receive circuitry housed in the back portion. In theembodiment illustrated in FIG. 10A, the interface to the MRI systemcomprises board 1072 for providing power, control and/or data betweenthe radio frequency apparatus and the MRI system and an adapter 1074constructed to prevent board 1072 from being connected to the MRI systemin an incorrect orientation. In this manner, foot coil 1030 can beeasily and simply connected to, operated by, and disconnected from theMRI system. Foot coil 1030 further comprises a base 1050 coupled to areleasable mechanism that allows the foot coil to engage with anddisengage from the MRI system. For example, as described in furtherdetail in connection with FIGS. 10C and 10D, base 1050 may be affixed toor otherwise coupled to a releasable mechanism that engages with acooperating member situated within the imaging region of the MRI system.

FIG. 10B illustrates another view of foot coil 1030 showing the nestedstructure of the exemplary foot coil. In particular, FIG. 10Billustrates receive housing 1030 r and transmit housing 1030 t beforeinsertion into outer housing 1030 a. In the exemplary foot coilillustrated in FIG. 10B, receive coil housing 1030 r (which supportsreceive coils 1090 b, 1090 b′ described below) is configured as theinner most housing providing the volume 1030 c adapted to accommodatethe foot. Transmit housing 1030 t is adapted to fit over receivedhousing 1030 r and the nested transmit/receive housing 1030 t/r isconfigured to be inserted into outer housing 1030 a. However, it shouldbe appreciated that the order of the nesting may be switched and/or asingle housing may be provided to support or carry both the transmit andreceive coils, as discussed in further detail below.

As visible in the view shown in FIG. 10B, transmit coil(s) 1090 a areprovided on transmit housing 1030 t and, more particularly, provided onan outside surface of the transmit housing. Alternatively oradditionally, transmit coil(s) 1090 a may be provided on an innersurface of transmit housing 1030 t, provided in grooves or contoursfabricated into the housing or otherwise integrated into transmithousing 1030 t. Transmit coil(s) 1090 a may comprise one or moreconductors arranged in a three-dimensional geometry about volume 1030 cto produce radio frequency pulses configured to cause MR signals to beemitted from a patient's foot positioned within volume 1030 c when footcoil 1030 is engaged with and operated by the MRI system. According tosome embodiments, transmit coil 1090 a comprises a single conductorprovided about transmit housing 1030 t in a number of turns over one ormore surfaces of the transmit housing. Alternatively, transmit coil 1090a may comprise multiple separate conductors provided over one or moresurfaces of transmit housing 1030 t.

In the embodiment illustrated in FIGS. 10A-D, transmit coil(s) 1090 aoperate as transmit only coils and the receive coils are provided as aseparate receive coil array, as discussed in further in detail inconnection with FIG. 10C. However, according to some embodiments, radiofrequency coil(s) 1090 a may also operate as one or more receive coilsconfigured to detect MR signals emitted from a foot being imaged inresponse to a selected pulse sequence produced, at least in part, by thesame coils operating in transmit mode. In such embodiments, radiofrequency coil(s) 1090 a operate as transmit and receive coils. Thegeometry of transmit coil(s) 1090 a (e.g., the relative spacing of theturns, the geometry of the contours, etc., may be determined togenerally optimize characteristics of the radio frequency pulses emittedbased on the geometry of volume 1030 c using, for example, any of thetechniques described in U.S. Patent Publication No. 2016/0334479,published Nov. 17, 2016 and titled “Radio Frequency Coil Methods andApparatus.” For example, a magnetic model may be used to determine ageometry for transmit coil(s) 1090 a that generally optimize themagnetic pulses delivered to volume 1030 c.

As discussed above, receive housing 1030 r may be configured to fitwithin transmit housing 1030 t. As visible in the view shown in FIG.10B, a plurality of receive coils 1090 b and 1090 b′ configured todetect magnetic resonance signals emitted from the foot of a patient inresponse to radio frequency pulses emitted by the transmit coils (e.g.,transmit coil(s) 1090 a) are provided on receive housing 1030 r. As withthe transmit coils, receive coils may alternatively or additionally beprovided on an inner surface of receive housing 1030 r or otherwiseintegrated within the housing. In the embodiment illustrated in FIGS.10B and 10C, the receive coils comprise eight separate receive coils;six receive coils 1090 b (e.g., three overlapping receive coils on eachside of receive housing 1030 r) and two receive coils 1090 b′ (e.g., areceive coil provided at least partially on top and bottom portions ofthe receive housing).

In the exemplary configuration illustrated in FIGS. 10B and 10C, thereceive coils 1090 b are positioned in an overlapping arrangement toreduce the inductive coupling between the coils. Spatially, receivecoils 1090 b are stacked in the vertical direction (e.g., in thedirection of the B₀ magnetic field illustrated generally by arrow 1025)with the same characteristic tilt of the foot coil. That is, the receivecoils may be aligned with the podal axis of the foot coil so that eachsuccessive receive coil is offset from the adjacent receive coil in ahorizontal direction (e.g., in the longitudinal direction. With thisarrangement, receive coils are configured to detect MR signals emittedfrom a patient's foot in directions along an axis orthogonal to the B₀magnetic field generated, for example, by the exemplary MRI systemsillustrated and described in the foregoing. Receive coils 1090 b′ arepositioned on the top and bottom sides of receive housing 1030 r togenerally detect magnetic resonance imaging signals emitted indirections along another axis orthogonal to the B₀ magnetic field. Inthis manner, the receive coils can be configured approximately asquadrature coils to generally optimize the detection of MR signals. Itshould be appreciated that receive coils 1090 b and 1090 b′ are merelyexemplary and any number of coils in any suitable arrangement may beused, as the aspects are not limited in this respect.

As shown in FIG. 10C, receive housing 1030 r includes a backside 1032 rhaving electronic connections to electronics 1070 on bottom portion 1030b′ that, when connected, allow power, control and/or data (e.g., MRsignal data) to be exchanged between the MRI system and the foot coil(e.g., between the MRI system and transmit coils 1090 a and receivecoils 1090 b, 1090 b′). Specifically, power, control and/or data may beexchanged via the connection cable 1076 and board 1072 when adapter 1074is connected to the MRI system in the manner discussed above inconnection with FIG. 10A.

The view in FIG. 10C shows base 1050 that supports the radio frequencycoil housings and releasable securing mechanism 1035 that, whenassembled, is coupled to the bottom of base 1050. According to someembodiments, releasable securing mechanism 1035 includes a retentionportion 1037 configured to grip a cooperating member affixed to the MRIsystem within the imaging region in a manner similar to or the same asthe securing mechanism discussed above in connection with the radiofrequency helmet described in FIGS. 7A-B and 8A-B. An example of oneembodiment of securing mechanism 1035 is described in further detail inconnection with the bottom view of foot coil 1030 illustrated in FIG.10D.

FIG. 10D illustrates a bottom view of foot coil 1030 showing securingmechanism 1035 configured to engage directly with an MRI system equippedwith a cooperating member to secure foot coil 1030 within the imagingregion of the MRI system, in accordance with some embodiments. Inparticular, in the embodiment illustrated in FIG. 10D, the outer housing1030 a may be coupled to base 1050 which in turn may be coupled toreleasable securing mechanism 1035 configured to engage with and grip acooperating member (e.g., member 729 illustrated in FIGS. 7A and 7B)attached to the MRI system at a location so that, when foot coil 1030 isengaged with the cooperating member, foot coil 1030 is positioned withinthe imaging region of the MRI system. In this manner, a patient's footpositioned within foot coil 1030 when attached to the MRI system isproperly positioned for imaging.

Exemplary releasable securing mechanism 1035 comprises a circularreceptacle portion dimensioned to accommodate the cooperating memberattached to the MRI system and a retention portion 1037 configured toresist movement of the cooperating member once the member has beenpositioned within the receptacle. Exemplary retention portion 1037comprises two arm portions 1037 a and 1037 b, respectively forming aportion of the receptacle and configured to grip the cooperating memberwhen positioned within the receptacle. According to some embodiments,arm portions 1037 a and 1037 b include protrusions 1033 a and 1033 b,respectively, configured to resist movement of the cooperating memberafter it has been inserted into the receptacle of releasable securingmechanism 1035. Protrusions 1033 a and 1033 b comprise respectiveoutward facing sides 1033 a′ and 1033 b′ and respective inward facingsides 1033 a″ and 1033 b″ dimensioned to facilitate securing thecooperating member of the MRI system to foot coil 1030.

According to some embodiments, the angle of the outward facing sides ofprotrusions 1033 a and 1033 b and the angle of the inward facing sidesof the protrusions are configured such that less forced is required toallow the cooperating member to enter into the receptacle of securingmechanism 1035 than is required to allow the cooperating member to exitthe receptacle (e.g., it requires less force to engage with thecooperating member than to disengage with the cooperating member). Forexample, as discussed above in connection with radio frequency helmet735, the relative angles of the outward and inward facing sides may beselected so that a relatively small force on the outward facing sides isneeded to part arm portions 1037 a and 1037 b to allow the cooperatingmember to enter the receptacle of releasable securing mechanism 1035 anda larger force on the inward facing sides is needed to part arm portions1037 a and 1037 b to allow foot coil 1030 to be released from thecooperating member (e.g., to allow the cooperating member to be releasedfrom the receptacle of securing mechanism 1035).

It should be appreciated that protrusions 1033 a and 1033 b may bedimensioned in any way so that desired forces achieve engaging anddisengaging securing mechanism 1035 with the cooperating member, as theaspects are not limited in this respect. Thus, foot coil 1030 can besecured to and released from the MRI system by applying a force in theappropriate direction. That is, securing mechanism 1035 is releasablebecause following engagement of arm portions 1037 a and 1037 b with thecooperating member, foot coil 1030 can released by providing sufficientforce on the foot coil so that the cooperating member forces the armportions 1037 a and 1037 b outward and releases the foot coil from thecooperating member. According to some embodiments, the cooperatingmember is similar to or the same as member 829 illustrated in FIGS. 8Aand 8B that includes a recess (e.g., recess 829 c) and the securingmechanism 1035 includes a pin or post (e.g., similar to or the same aspin 831 illustrated in FIGS. 8A and 8B) so that the foot coil can berotated about the cooperating member until the pin finds the recess andprevents further rotation.

FIG. 11 illustrates a foot coil adapted for a larger foot, for example,a swollen foot resulting from disease such as diabetes or complicationsthat causes edema (e.g., congestive heart failure, kidney or liverdisease, etc.), swelling that results from infection or trauma, or thefoot of a larger person. Foot coil 1130 may be similar in many respectsto foot coil 1030 illustrated in FIG. 10A. However, foot coil 1130 isconstructed to have a width W that is greater than the width w of coil1030 illustrated in FIG. 10A to accommodate a larger foot and, moreparticularly, a larger width foot characteristic of disease or edema,thus providing a larger volume 1130 c for the foot coil 1130. Asdiscussed above, the angle at which foot coil is tilted relative tovertical may be selected based on patient comfort, to accommodate largerfeet, to accommodate other circumstances or imaging conditions, etc.Similarly, the podal axis of foot coil 1130 illustrated in FIG. 11 mayalso be varied for comfort and/or to accommodate longer feet. Similarly,different foot coils may be manufactured at different angles so that awide variety of patients and imaging conditions can be accommodated.

FIG. 12A illustrates a foot coil 1230 engaged with a cooperating memberof MRI system 1200 so that the foot coil 1230 and the right footpositioned therein is within the imaging region of MRI system 1200 andpositioned correctly for imaging. FIGS. 12B and 12C illustrate differentviews of the foot coil 1230 positioned with MRI system 1200. FIG. 12Dillustrates foot coil 1230 accommodating the left foot. Also, FIG. 12Dshows support 1231 (also visible in FIGS. 12A-12C) inserted within footcoil 1230 to support and provide comfort to the foot during an imagingprocedure.

As discussed above, imaging a patient using MRI from, for example, astandard hospital bed typically requires positioning target anatomy ofthe patient within an MRI system located proximate the hospital bed onwhich the patient is lying. As discussed in connection with FIGS. 4A-I,the inventors have developed techniques for facilitating the positioningof a patient within the MRI system for imaging of desired anatomy of thepatient from the patient's bed. For example, FIG. 4A illustrates aportable low-field MRI system 400 that has been moved into positionproximate a standard hospital bed 490 to perform MRI on a patient 499who may be confined to the bed for convenience, comfort or stabilizationand/or because the patient is unconscious, immobilized or otherwise isnot ambulatory or cannot be safely moved. Portable MRI system 400 may bea local installation deployed in an emergency room, operating room,intensive care unit, doctor's office, etc. that can be moved to bed 490,or in some cases, bed 490 can be wheeled to the MRI system. As discussedin detail in the foregoing, because of the low-field strengths of MRIsystem 400, bed 490 can be safely positioned in close proximity to MRIsystem 400.

To bridge the gap between bed 490 and MRI system 100, the MRI system maybe equipped with a bridge 473 mounted to MRI system 100 to facilitatepositioning patient 199 within the imaging region of MRI system 100.Specifically, bridge 473 provides a surface 474 over which patient 499can be moved so that the patient's anatomy being imaged (e.g., thepatient's head) can be positioned within the imaging region of the MRIsystem. However, the inventors have recognized that exemplary bridge 473illustrated in FIG. 4A may be improved in a number of ways. For example,bridge 473 may be designed to work in cooperation with patient support440 so that as long as the bridge 473 has dimension suitable to allowedthe patient support to be transitioned over its surface, the dimensionsof the bridge are sufficient. However, in some embodiments, a patientmay be positioned within MRI system 400 without the assistance of apatient support. In such embodiments, it may be preferable to employ alarger dimensioned bridge both to facilitate ease and comfort ofpositioning the patient and to accommodate larger and heavier patients.The inventors have developed bridges adapted to facilitate patientpositioning that are generally optimized for use either with or withouta patient support.

As illustrated in FIG. 4A, fixed bridge 473 protrudes out from the MRIsystem, thereby increasing the footprint of the system. As a result,navigating the MRI system down hallways and through doorways is moredifficult. Additionally, the useable surface of bridge 473 is limitedand the construction of the bridge may not be suitable for heavierpatients, particularly in cases where the patient is being positionedwithout the aid of a patient support. As a result, bridge 473 may bedifficult to use with larger and/or heavier patients and may not berated to support the heaviest patients. However, increasing thedimensions of the bridge to facilitate patient positioning without apatient support and/or to support heavier or larger patient, results ina bridge that protrudes even further from the MRI system and requiresmore robust construction.

The inventors have recognized the benefits of patient support bridgecapable of supporting larger and heavier patients and have appreciatedthe benefits of such a bridge that can accommodate a range of gapsbetween the MRI system and a patient bed and/or that provide moreoverlap between the bridge and the bed. Specifically, for patientcomfort, safety and/or to facilitate more convenient positioning of apatient, particularly larger and/or heavier patients, it is desirable toequip a portable MRI system with relatively large dimensioned bridgescapable of safely supporting a wide range of patients. However, thereare a number of issues associated with the design and development ofrelatively large dimensioned bridges capable of supporting the weight oflarger patients.

For example, as mentioned above, larger bridges increase the footprintof the MRI system even further, making it more difficult (or impossible)to transport the MRI system down hallways and to fit the MRI systemthrough the doorways of the health care facilities in which they aredeployed. To address the problem of increased footprint for the MRIsystem, the inventors have developed a fold-out bridge that can befolded-down to facilitate positioning the patient within the imagingregion of the MRI system and to support the patient during an imagingprocedure and that can be folded-up during transport of the MRI systemso that the MRI system can be more easily moved down hallways andthrough doorways to the patient.

Additionally, providing a bridge capable of safely supporting larger,heavier patients requires robust construction. Typically, such patientsupports would be constructed using large amounts of metal materialcapable of withstanding the significant stresses resulting fromsupporting the weight of heavier patients. However, significantquantities of metal may negatively impact the operation of the magneticresonance imaging system to which the bridge is attached by distortingthe main magnetic field and/or producing substantial eddy currentsduring operation of the magnetic resonance imaging system thatnegatively impact image quality. To mitigate this problem, someembodiments include a fold-up bridge in which the metal composition ofthe bridge is minimized to the extent possible to provide a bridgecapable of supporting heavier patient while minimizing the impact on theoperation of the magnetic resonance imaging system. Thus, the exemplaryfold-up bridges described herein may be capable of supporting largeand/or heavy patients safely and securely, thus taking advantage of thebenefits of larger dimensioned bridges without significantly impactingthe ability to move the MRI system down hallways and through doorways.

Following below are more detailed descriptions of various conceptsrelated to, and embodiments of, a fold-out bridge that can be moved froma vertical position for stowing during transport of a portable low-fieldMRI system or when the MRI system is not in use to a horizontal positionto facilitate positioning of the patient for point-of-care MRI. Itshould be appreciated that the embodiments described herein may beimplemented in any of numerous ways. Examples of specificimplementations are provided below for illustrative purposes only. Itshould be appreciated that the embodiments and the features/capabilitiesprovided may be used individually, all together, or in any combinationof two or more, as aspects of the technology described herein are notlimited in this respect or to the specific combinations described.

FIGS. 13A and 13B illustrate an exemplary fold-out bridge for supportinga patient during positioning and imaging, in accordance with someembodiments. Bridge 1300 is configured to be placed in a stowed or“folded-up” position (also referred to simply as the “up” or “vertical”position) or placed in an operational or “folded-down” position (alsoreferred to simply as the “down” or “horizontal” position),respectively. Bridge 1300 includes a support 1310 configured to bridge agap between the MRI system to which the bridge is attached and, forexample, a hospital bed to which the MRI system is proximately located.Support 1310 comprises a surface 1310 a designed to support the patientduring positioning and imaging when the bridge is placed in the downposition shown in FIG. 13B.

When bridge 1300 is in the down position, surface 1310 a of support 1310is substantially horizontal to provide support for the patient. Support1310, and particularly surface 1310 a, may be made of material thatreduces friction between a patient and the bridge, such as a smoothplastic, to facilitate positioning of the patient within the imagingregion of the MRI system without producing eddy currents duringoperation of the system. As shown in FIG. 13A, when bridge 1300 is inthe up position, surface 1310 a (which is visible in FIG. 13B) ofsupport 1310 is substantially vertical so that the support does not addsubstantially, if at all, to the dimensions of the magnetic resonanceimaging system (e.g., when the bridge is in the up position, the bridgedoes not increase the outer perimeter or footprint of the system).

Bridge 1300 comprises a hinge 1350 that allows support 1310 to pivotfrom the up position to the down position and vice versa (e.g., hinge1350 allows bridge 1300 to be moved between the positions illustrated inFIGS. 13A and 13B). According to some embodiments, hinge 1350 comprisesa shaft 1355 that allows support 1310 to pivot or rotate from thevertical position shown in FIG. 13A to the horizontal position shown inFIG. 13B and vice versa. Specifically, exemplary bridge 1300 comprises abase 1352 and a pivot portion 1358 through which shaft 1355 passes toallow the pivot portion 1358 to rotate about the shaft when folding upand folding down the bridge. Base 1352 is configured to attach to theMRI system and includes stop 1353 (see FIG. 13A) and stop 1354 (see FIG.13B) that provide end stops to prevent further pivoting of the bridgewhen the horizontal position and vertical position are reached,respectively.

Base 1352 further comprises counter-bores 1345 (e.g., bores 1345 a, 1345b and 1345 c) to accommodate bolts that allow bridge 1300 to be securelyattached to the MRI system. For example, according to some embodiments,base 1352 is constructed with three counter-bores to accommodaterespective M8 bolts that securely attach the base of the bridge directlyto the B₀ magnet of the MRI system (e.g., as shown in FIGS. 17A-17Cdiscussed below). Bolting the bridge to the MRI system in this mannercontributes to the bridge being able to withstand the torque produced bythe weight of a patient.

As discussed above, the inventors have recognized the benefits ofproviding a bridge that can accommodate larger (e.g., wider) and heavierpatients and that can bridge larger gaps between a patient bed and theMRI system and/or that provide additional overlap with the patient bedwhen placed in the down position. According to some embodiments, afold-out bridge is constructed having a width of between 12 and 36inches and a length of between 8 and 24 inches. For example, exemplarybridge 1300 has a width W of at least 24 inches and a length L of atleast 12 inches to provide a relatively large surface to accommodate avariety of patients and to bridge a variety of gaps. The length of thebridge refers to the dimension generally in a direction outward from theMRI system. By increasing the length of the bridge, larger gaps can bebridged and/or larger overlaps with a patient bed can be achieved.

The width of the bridge refers to the dimension generally in a directiontangent to the MRI system. By increasing the width of the bridge, widerpatients may be more comfortably accommodated and supported. Hospitalequipment for acute care is often rated to accommodate patients weighing500 lbs. (e.g., hospital beds are often rated to support 500 lb.patients). According to some embodiments, bridge 1300 is also rated for500 lb. patients and may be constructed to have a safety factor of atleast 2.5 (i.e., that have a yield strength of at least 2.5 times therating). According to some embodiments, bridge 1300 is rated for 500 lb.patients and is constructed to have a safety factor of 4.0 or more,examples of which are described in further detail below.

FIG. 14 illustrates components of a fold-out bridge 1400 to illustrateexemplary construction details, in accordance with some embodiments.Similar to bridge 1300 described above, bridge 1400 includes a support1310 having a surface 1310 a configured to support a patient duringpositioning and imaging. Bridge 1400 further includes a hinge 1350comprising base 1352 and pivot portion 1358 that, when coupled togethervia shaft 1355, allows support 1310 to pivot from a vertical position toa horizontal position and vice versa. For exemplary bridge 1400, support1310 may be coupled to pivot portion 1358 using a tongue-and-grooveinterface. Specifically, support 1310 includes a groove 1317 configuredto receive tongue 1357, which extends out from pivot portion 1358. Tocouple the support to the pivot portion, tongue 1357 may be insertedinto groove 1317 and screwed or bolted into place to secure support 1310to pivot portion 1358.

To construct hinge 1350, pivot portion 1358 comprises shoulders 1359 aand 1359 b between which is provided gap 1363 sized to accommodate base1352. Shoulders 1359 a, 1359 b and stop 1354 of base 1352 includecooperating bores 1365 through which shaft 1355 is inserted to allowsupport 1310 to pivot between the up and down positions. Whenconstructed, shaft 1355 is secured within bores 1365 of the base andpivot portions with nuts 1366 a and bolts 1366 b at both ends of theshaft. Thus, pivot portion 1358 is allowed to rotate about the shaft sothat support 1310 can be moved from the vertical position (i.e., inwhich planar surface 1310 a is substantially vertical) when not in useto the horizontal position (i.e., in which the planar surface 1310 a issubstantially horizontal) to facilitate positioning a patient within theimaging region of the MRI system and to support the patient duringimaging. As discussed above, bridge 1400 can be bolted to the MRI systemvia bolt holes 1345 a-c (e.g., bolted to the lower B₀ magnet of the MRIsystem so that it is level with the patient surface within the imagingregion of the MRI system as shown in FIGS. 6A-C discussed below).

Bridge 1400 may further include ball plungers 1380 a and 1380 b thatfacilitate holding the bridge in the vertical position when the bridgeis not being used. For example, ball or spring plungers 1380 a and 1380b may be positioned on either side of base 1352 to interact withshoulders 1359 a and 1359 b of pivot portion 1358. Specifically, to movebridge 1400 from the vertical to the horizontal position, the shouldersof the pivot portion must first overcome the resistance provided by thespring loaded ball plungers (i.e., to pivot bridge 1400 out of thevertical position, shoulders 1359 a and 1359 b must first move over theball plungers, which provide a counter-resistance to the initialrotation of the pivot portion). Accordingly, because an initial forceexceeding the resistance of the ball plungers is needed to move thebridge out of the vertical position, a measure of safety is provided byreducing the chances that bridge 1400 will unintentionally fall from thevertical position to the horizontal position. Bridge 1400 may alsoinclude rubber stoppers 1393 configured to fit within correspondingholes provided in stop 1353 of base 1352 to reduce noise produced whenshoulders 1359 a, 1359 b contact stop 1353 when the bridge is moved tothe down position and/or to absorb some of the impact of the bridgeshould the bridge fall or if the bridge is roughly handled duringtransition to the horizontal position.

FIG. 15A illustrates a model of a fold-out bridge 1500 constructed tosupport larger and/or heavier patients, in accordance with someembodiments. The model illustrated in FIG. 15A was used to perform anumber of performance tests on exemplary bridge 1500 designed to providea relatively large surface to facilitate patient positioning andconstructed to support heavier patients (e.g., to achieve a 500 lb.rating). The following dimensions, materials and construction detailsare provided merely as description of exemplary bridge 1500 on whichstress tests were performed and do not limit the aspects of a fold-outbridge in this respect. In particular, different dimensions, materialsand designs may be used to construct a fold-out bridge and differentaspects of a fold-out bridge discussed herein may be used in differentcombinations. Bridge 1500 merely illustrates one example of a suitablefold-out bridge capable of supporting larger and/or heavirt patients andthat provides a relatively large surface to facilitate patientpositioning and support.

Bridge 1500 is provided with a support 1310 having a relatively largesurface area, for example, a width of 24 inches and a length of 14.4inches measured from the far side of support 1310 to the center of thecurved interface of base 1352 where bridge 1500 is bolted to the MRIsystem (i.e., at counter-bore 1345 b). Support 1310 is formed, at leastin part, by a 1 inch thick plastic platform that provides a surface 1310a over which a patient can be moved to position the patient within theMRI system. Similar to the construction of exemplary bridge 1400, pivotportion 1358 is coupled to support 1310 via a tongue-and-grooveinterface and coupled to the base via a 16 mm diameter shaft 1355inserted through shoulder portions 1359 a and 1359 b. For exemplarybridge 1500, shoulders 1359 a and 1359 b are constructed of metal (e.g.,aluminum) and tongue portion 1357 is constructed of plastic (or othernon-metallic material). Base 1352 for exemplary bridge 1550 isconstructed of metal, such as steel, and comprises three counter-bores1345 a-c for bolting bridge 1500 to the B₀ magnet of the MRI system(e.g., using three corresponding M8 bolts). In this way, components ofbridge 1500 that undergo the greatest amount of stress may beconstructed of metal and components that undergo less stress may be madeof plastic (or other non-metallic material) to minimize eddy currentproduction when the MRI system is operated, while providing a bridgewith a robust construction.

To evaluate the performance of exemplary bridge 1500, stress tests weresimulated on the model of bridge 1500 to ensure that the design achievesa 500 lb. rating with a safety factor suitable for patient supportequipment. In particular, using the above described constructiondetails, a mesh was applied to the model of bridge 1500 as shown in FIG.15A and the stresses resulting from the weight of a patient weresimulated via finite element analysis. The weight that bridge 1500 isrequired to support for a 500 lb. patient was obtained from theInternational Electrotechnical Commission (IEC) 60601-1 InternationalStandard. Specifically, IEC 60601-1 establishes a number of safetyrequirements and performance standards for medical equipment.

Figure A.19 of IEC 60601-1, which is reproduced herein as FIG. 15D,shows an example of human body mass distribution that was used todetermine how the weight of a 500 lb. patient is distributed over thepatient support surface of the exemplary bridges described herein. Asshown in FIG. 15D, Figure A.19 of IEC 60601-1 specifies the lengthdimension (in millimeters) and the percent of a patient's body mass thatis contributed by significant segments of the human body lying in asupine position. Specifically, the head accounts for 7.4% of the mass ofthe patient, the torso accounts for 40.7%, the upper arms togetheraccount for 7.4% and the lower arms another 7.4%, the upper legs accountfor 22.2% and the lower legs account for 14.8%. When a patient ispositioned within a portable MRI system, the head lies within theimaging region and is supported by the MRI system (e.g., by the helmeton which the transmit/receive coils are located) so that the bridge needsupport at least some portion of the torso, shoulder and arm portions ofthe body. The full contribution of the torso and the upper arms isapproximately 50% (48.1%) of the body mass of the patient. Accordingly,in approximate numbers, for a bridge having a 500 lb. rating and asafety factor of 1, the bridge would be required to support 250 lbs.(i.e., 50% of the patient's total weight). For a safety factor of 2.5,the bridge would need to support 625 lbs (i.e., 50% of the patient'sweight times 2.5) and, for a safety factor of 4, the bridge would needto support 1000 lbs. (i.e., 50% of the patients weight times 4).

To evaluate bridge 1500 for a 500 lb. rating, the stresses on bridge1500 resulting from a 500 lb. patient were simulated by distributing 250lbs. of weight over the surface of the bridge (i.e., 50% of thepatient's weight that the bridge needs to support), as shown by thedownward arrows in FIGS. 15A-15C. Using the materials and dimensionsdiscussed above, this distributed weight produced the stress plot shownin FIG. 15B. A maximum stress of 6,981 psi resulted at the corners ofthe base indicated by arrows 1553 a and 1553 b. The yield strength ofexemplary bridge 1500 was also assessed to evaluate the maximum stressthat bridge 1500 can withstand. The yield strength of bridge 1500 wasdetermined to be 30,000 psi. Thus, exemplary bridge 1500 achieves a 500lb. rating with a safety factor of 4.3. Specifically, the yield strengthof the bridge is 4.3 times greater than the maximum stress resultingfrom simulating the forces applied on bridge 1500 by a 500 lb. patient.

FIG. 15C illustrates a deflection plot showing the deformation of thebridge under the 250 lb. simulated weight. The maximum deflection of thebridge resulting from the simulation was 1.5 mm at the far end ofsupport 1310. In particular, the arrows show the location of the bridgewithout the simulated force applied. In FIGS. 15B and 15C, thedisplacement resulting from the applied 250 lbs. is shown at 36.4 scaleto exaggerate the displacement so that it can be visualized (i.e., theactual displacement is 36.4 times smaller than it appears in the plotsshown in FIGS. 15B and 15C.). Thus, a 250 lb. weight distributed acrossbridge 1500 to simulate the stresses resulting from a 500 lb. patientresulted in a maximum displacement of 1.5 mm at end 1310 b of support1310.

The inventors have recognized that some embodiments of a fold-out bridgemay be relatively large and heavy, particularly when dimensioned andconstructed to facilitate positioning and support of larger, heavierpatients. For example, an exemplary bridge may be dimensioned to have alength of between 1 and 2 feet or more and a width of between 1.5 and2.5 feet or more, resulting in bridges that can weigh between 8 and 15lbs. or more. Larger, heavier bridges have the potential to injure ifthe bridge accidentally falls from the vertical position. To prevent abridge from being able to free fall, the inventors have developed acounter-balance mechanism configured to slow the rate at which thebridge can transition from the up position to the down position. Thecounter-balance mechanism provides an additional safety precaution thatprotects patients and medical personnel from possible injury, asdiscussed in further detail below.

FIGS. 16A and 16B illustrate components for a bridge 1600, in accordancewith some embodiments. Exemplary fold-out bridge 1600 may comprise manyof the same components described in connection with bridge 1400illustrated in FIG. 14 and/or bridge 1500 illustrated in FIGS. 15A-C.However, bridge 1600 includes a counter-balance mechanism configured toslow the rate at which fold-out bridge 1600 can pivot to the horizontalposition. According to some embodiments, the counter-balance mechanismcomprises torsion springs 1375 a and 1375 b. Torsion springs 1375 a and1375 b are configured to fit over respective ends of shaft 1655. Eachtorsion spring 1375 a, 1375 b is configured with end portions 1376 a and1376 b that protrude out from the spring in the direction of the shaft'slongitudinal axis, as can be seen best in the magnified portion of oneend of the counter-balance component illustrated in FIG. 16B.

In particular, end portions 1376 a are arranged in the direction of theaxis of shaft 1655 and positioned on the perimeter of the respectivetorsion spring and are configured to fit into a corresponding indexinghole 1378 provided in indexing components 1377 a, 1377 b. End portions1376 b are similarly arranged and configured to fit into respectiveindexing holes 1378 provided in shoulders 1659 a and 1659 b of pivotportion 1658. Specifically, indexing components 1377 a, 1377 b comprisea plurality of indexing holes 1378 around the perimeter (see e.g.,exemplary indexing holes 1378 a and 1378 b illustrated in FIG. 16B) toaccommodate end portions 1376 a. Shoulders 1659 a and 1659 b comprisenotches 1656 a and 1656 b to accommodate respective torsion springs.Notches 1656 a and 1656 b comprise bores 1365 through which shaft 1655passes and further comprise indexing holes 1378 into which end portions1376 b are inserted (as best seen by indexing hole 1378 d provide nextto bore 1365 within notch 1656 b). For example, end portion 1376 b ofeach torsion spring 1375 a, 1375 b fits into the respective indexingholes 1378 c and 1378 d so that the torsion spring is coupled toindexing component 1377 at one end and pivot component 1658 at the otherend.

Shaft 1655 includes flats 1655 a and 1655 b configured to fit intorespective indexing components 1377 a and 1377 b. Specifically, flats1655 a and 1655 b are configured to be inserted into slots 1379 providedin respective indexing components 1377 a, 1377 b (as seen best in themagnified view shown in FIG. 16B) and secured by screws 1666 a and 1666b at opposite ends of shaft 1655. To facilitate operation of thecounter-balance mechanism, corresponding screw holes 1336 a and 1336 bare provided through stop 1354 of base 1352 and into shaft 1655,respectively, to accommodate screw 1335 to hold shaft 1355 in place.Specifically, screw 1335 is inserted through screw hole 1336 a in thebase and into screw hole 1336 b in shaft 1655 to prevent the shaft fromrotating when pivot portion 1658 rotates during transitions between theup and down positions. Preventing shaft 1355 from rotating ensures thatrotation of pivot portion 1658 causes the torsion springs 1375 a, 1375 bto wind-up or tighten to slow the rate at which pivot portion 1658 canrotate, as discussed in further detail below. Sleeves 1360 a and 1360 bcover respective torsion springs 1375 a and 1375 b when the bridge isassembled.

When constructed as described above, shaft 1655 is fixed in place andprevented from rotating by inserting the shaft through bores 1365 andinto slots 1379 of the respective indexing portions 1377 a, 1377 b andscrewing the shaft in place via screws 1666 a, 1666 b and 1335. Byinserting end portions 1376 a and 1376 b of the torsion springs 1375 a,1375 b into the indexing portions 1377 a, 1377 b and pivot portion 1658,respectively, rotation of pivot portion 1658 from the vertical positionto the horizontal position causes the torsion springs to tighten due tothe fixed connection between end portions 1376 a and the indexingcomponents 1377 a, 1377 b (which does not rotate) and the fixedconnection between end portions 1376 b and the indexing holes 1378 c,1378 d in notches 1656 a, 1656 b, respectively, by which end portions1376 b are rotated along with the pivot portion 1658. That is, becauseindexing holes 1378 c and 1378 d and end portions 1376 b are aligned inthe direction of the shaft axis but are positioned off-axis, therotation of the pivot portion causes the torsion spring to tighten asindexing holes 1378 c and 1378 d rotate about the axis of the shaft.Thus, when the bridge pivots from a vertical to a horizontal position,the twisting of the torsion springs slows the rotation of support 1310to prevent the bridge from rotating in free fall. The spring constant ofthe torsion springs can be selected to achieve the desired level ofcontrol of the rate at which the bridge is allowed to transition betweenthe up and down positions. In this manner, bridge 1600 includes acounter-balance mechanism providing an additional safety mechanism toreduce the chances of injury when using a fold-out bridge.

As discussed above, the exemplary fold-out bridges described herein areconfigured to attach to a portable magnetic resonance imaging system tofacilitate positioning and supporting a patient during point-of-careMRI. FIGS. 17A, 17B and 17C illustrate a portable low-field MRI systemto which the exemplary fold-out bridges described herein can beattached. Specifically, portable low-field MRI system 10000 can bedeployed in virtually any environment to image patients, for example,from a standard hospital bed located in emergency rooms, intensive careunits, operating rooms, neonatal units, clinics, primary care offices,recovery units, etc. where conventional MRI is typically not available.Exemplary fold-out bridge may be configured to facilitate positioningand support of large, heavy patients without substantially increasingthe footprint of the MRI system by virtue of being capable of beingstowed in the vertical position during transport or when not in use andfolded-down when needed to perform, for example, point-of-care MRI.

In particular, to facilitate transporting portable MRI system 10000 tolocations at which MRI is needed, portable MRI system 10000 is equippedwith a fold-out bridge 1700, which may include any one or more of thefeatures of a fold-out bridge described herein. FIG. 17A illustratesbridge 1700 configured in its up position so that support 1710 issubstantially vertical and does not add significantly (or at all) to thefootprint of the MRI system. As a result, bridge 1700 does not impedemoving the portable MRI system down hallways and through doorways. FIG.17A also illustrates a deployable guard 10040 in its deployed positionto indicate the 5-Gauss line for the MRI system as its being transportedor when it is stored away or otherwise not in use. As discussed in U.S.application Ser. No. 16/389,004, titled “Deployable Guard for PortableMagnetic Resonance Imaging Device,” filed on Apr. 19, 2019, and which isherein incorporated by reference in its entirety, the guard can bedeployed to demarcate the physical boundary within which the magneticfield is above a specified field strength to provide a visual signalregarding the magnetic field when the MRI system is being moved to adifferent location. In addition, as illustrated in FIG. 17B, when bridge1700 is up, the bridge provides a barrier to the imaging region of theMRI system where the magnetic field is strongest.

FIG. 17B illustrates portable MRI system 10000 with bridge 1700configured in the down position and FIG. 17C illustrates bridge 1700deployed in the down position to bridge the gap between a patient bed490 and MRI system 10000 to allow patient 499 to be positioned withinthe imaging region of the MRI system and to support patient 499 duringimaging. As discussed above, bridge 1700 may be bolted to the B₀ magnetto secure the bridge to the MRI system. For example, as shown in FIG.17B, portable MRI system 10000 comprises a B₀ magnet 10005 that includesat least one first permanent B₀ magnet 10010 a and at least one secondpermanent B₀ magnet 10010 b magnetically coupled to one another by aferromagnetic yoke 10020 configured to capture and channel magnetic fluxto increase the magnetic flux density within the imaging region 10065(field of view) of the MRI system. For exemplary MRI system 10000,bridge 1700 is bolted to the lower magnet 10010 b so that when it isdeployed (i.e., positioned in the down position as shown in FIGS. 17Band 17C), support 1710 provides a continuation of the planar surface10015 of the magnet housing to facilitate positioning the patient withinimaging region 10065 and providing relatively level support to thepatient during imaging. FIG. 17B also illustrates a conveyance mechanism10080 of MRI system 10000 that facilitates moving the MRI system fromone location to another, as discussed in further detail below.

FIG. 17C illustrates patient 499 positioned within the imaging region ofMRI system 1000 for imaging of the patient's head from hospital bed 490.As shown, once the patient is positioned with the imaging region andduring the imaging process, the patient's head is supported by helmet10030 (which comprises radio frequency transmit and receive coils), atleast a portion of the patient's torso and arms are supported byfold-out bridge 1700 and the remainder of the patient's weight issupported by patient bed 490. As discussed above, some embodiments of afold-out bridge are dimensioned and constructed to support large andheavy patients. For example, bridge 1700 may be rated for a 500 lb.patient with a safety factor of 2.5 or more. According to someembodiments, bridge 1700 may be rated for a 500 lb. patient with asafety factor of 4.0 or more (e.g., a safety factor of 4.3), forexample, using the various exemplary bridge constructions describedabove in connection with any of exemplary bridges 1400, 1500 or 1600.

As discussed above, portable MRI system 10000 includes a conveyancemechanism configured to allow the portable MRI system to be transportedto desired locations. Referring to FIG. 17B, portable MRI system 10000comprises a conveyance mechanism 10080 having a drive motor 10086coupled to drive wheels 10084. Conveyance mechanism 10080 may alsoinclude a plurality of castors 1082 to assist with support and stabilityas well as to facilitate transport of the MRI system. In this manner,conveyance mechanism 10080 provides motorized assistance in transportingMRI system 10000 to desired locations.

According to some embodiments, conveyance mechanism 10080 includesmotorized assistance controlled using a controller (e.g., a joystick orother controller that can be manipulated by a person) to guide theportable MRI system during transportation to desired locations.According to some embodiments, the conveyance mechanism comprises powerassist means configured to detect when force is applied to the MRIsystem and to engage the conveyance mechanism to provide motorizedassistance in the direction of the detected force. For example, rail10050 illustrated in FIG. 17B may be configured to detect when force isapplied to the rail (e.g., by personnel pushing on the rail) and engagethe drive motor to provide motorized assistance to drive the wheels inthe direction of the applied force. As a result, a user can guide theportable MRI system with the assistance of the conveyance mechanism thatresponds to the direction of force applied by the user. The drive motormay be operated in other ways, such as via buttons, roller ball or othersuitable mechanism located on the MRI system, or using touch screencontrols on a mobile computing device 10025 communicatively coupled tothe MRI system, as the aspects of motorized control is not limited inthis respect.

Thus, low-field MRI system 10000 equipped with fold-out bridge 1700 canbe used to perform point-of-care MRI on a patient, including large andheavy patients. For example, to perform point-of-care MRI on a patientfrom a standard medical bed, the MRI system and the bed can bepositioned proximate one another. In some embodiments, the MRI system isportable and can be moved into position near the hospital bed by medicalpersonnel pushing the MRI system into place and/or using a motor driveconveyance system to move the MRI system into position. In someinstances, the MRI system may need to be transported from another roomor unit within the hospital. In other instances, the MRI system mayalready be located in the same room as the patient and need only bemoved next to the bed of the patient. In other circumstances, a hospitalbed is transported to the MRI system and moved into place proximate theMRI system for imaging. During the positioning of the MRI system and thepatient bed near one another, a fold-out bridge attached to the MRIsystem may be positioned in the vertical or up position (e.g., in thevertical position illustrated in FIG. 17A) to facilitate transport ofthe system down hallways and/or through doorways and/or to facilitatepositioning the MRI system and the bed in close proximity (e.g.,positioning the MRI system and the foot or head of the bed adjacent oneanother).

Once the MRI system and the bed are positioned proximate one another,the fold-out bridge may be moved from the vertical position to ahorizontal position so that the bridge at least partially overlaps thebed (e.g., the fold-out bridge 1700 may be moved from the verticalposition illustrated in FIG. 17A to the horizontal position illustratedin FIGS. 17B and 17C). The fold-out bridge then provides a surface thatbridges the gap between the MRI system and the bed over which thepatient can be moved. For example, the portion of anatomy of the patientto be imaged may be positioned within an imaging region of the MRIsystem via the bridge and the bridge may provide support for the patientduring and after positioning the patient within the imaging region.After positioning the patient within the MRI system, at least onemagnetic resonance image of the portion of the anatomy of the patientmay be acquired while the patient is at least partially supported by thebed and at least partially support by the bridge (e.g., as shown in FIG.17C). In this way, point-of-care MRI may be performed.

Having thus described several aspects and embodiments of the technologyset forth in the disclosure, it is to be appreciated that variousalterations, modifications, and improvements will readily occur to thoseskilled in the art. Such alterations, modifications, and improvementsare intended to be within the spirit and scope of the technologydescribed herein. For example, those of ordinary skill in the art willreadily envision a variety of other means and/or structures forperforming the function and/or obtaining the results and/or one or moreof the advantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the embodimentsdescribed herein. Those skilled in the art will recognize, or be able toascertain using no more than routine experimentation, many equivalentsto the specific embodiments described herein. It is, therefore, to beunderstood that the foregoing embodiments are presented by way ofexample only and that, within the scope of the appended claims andequivalents thereto, inventive embodiments may be practiced otherwisethan as specifically described. In addition, any combination of two ormore features, systems, articles, materials, kits, and/or methodsdescribed herein, if such features, systems, articles, materials, kits,and/or methods are not mutually inconsistent, is included within thescope of the present disclosure.

The above-described embodiments can be implemented in any of numerousways. One or more aspects and embodiments of the present disclosureinvolving the performance of processes or methods may utilize programinstructions executable by a device (e.g., a computer, a processor, orother device) to perform, or control performance of, the processes ormethods. In this respect, various inventive concepts may be embodied asa computer readable storage medium (or multiple computer readablestorage media) (e.g., a computer memory, one or more floppy discs,compact discs, optical discs, magnetic tapes, flash memories, circuitconfigurations in Field Programmable Gate Arrays or other semiconductordevices, or other tangible computer storage medium) encoded with one ormore programs that, when executed on one or more computers or otherprocessors, perform methods that implement one or more of the variousembodiments described above. The computer readable medium or media canbe transportable, such that the program or programs stored thereon canbe loaded onto one or more different computers or other processors toimplement various ones of the aspects described above. In someembodiments, computer readable media may be non-transitory media.

The terms “program” or “software” are used herein in a generic sense torefer to any type of computer code or set of computer-executableinstructions that can be employed to program a computer or otherprocessor to implement various aspects as described above. Additionally,it should be appreciated that according to one aspect, one or morecomputer programs that when executed perform methods of the presentdisclosure need not reside on a single computer or processor, but may bedistributed in a modular fashion among a number of different computersor processors to implement various aspects of the present disclosure.

Computer-executable instructions may be in many forms, such as programmodules, executed by one or more computers or other devices. Generally,program modules include routines, programs, objects, components, datastructures, etc. that perform particular tasks or implement particularabstract data types. Typically the functionality of the program modulesmay be combined or distributed as desired in various embodiments.

Also, data structures may be stored in computer-readable media in anysuitable form. For simplicity of illustration, data structures may beshown to have fields that are related through location in the datastructure. Such relationships may likewise be achieved by assigningstorage for the fields with locations in a computer-readable medium thatconvey relationship between the fields. However, any suitable mechanismmay be used to establish a relationship between information in fields ofa data structure, including through the use of pointers, tags or othermechanisms that establish relationship between data elements.

The above-described embodiments of the present invention can beimplemented in any of numerous ways. For example, the embodiments may beimplemented using hardware, software or a combination thereof. Whenimplemented in software, the software code can be executed on anysuitable processor or collection of processors, whether provided in asingle computer or distributed among multiple computers. It should beappreciated that any component or collection of components that performthe functions described above can be generically considered as acontroller that controls the above-discussed function. A controller canbe implemented in numerous ways, such as with dedicated hardware, orwith general purpose hardware (e.g., one or more processor) that isprogrammed using microcode or software to perform the functions recitedabove, and may be implemented in a combination of ways when thecontroller corresponds to multiple components of a system.

Further, it should be appreciated that a computer may be embodied in anyof a number of forms, such as a rack-mounted computer, a desktopcomputer, a laptop computer, or a tablet computer, as non-limitingexamples. Additionally, a computer may be embedded in a device notgenerally regarded as a computer but with suitable processingcapabilities, including a Personal Digital Assistant (PDA), a smartphoneor any other suitable portable or fixed electronic device.

Also, a computer may have one or more input and output devices. Thesedevices can be used, among other things, to present a user interface.Examples of output devices that can be used to provide a user interfaceinclude printers or display screens for visual presentation of outputand speakers or other sound generating devices for audible presentationof output. Examples of input devices that can be used for a userinterface include keyboards, and pointing devices, such as mice, touchpads, and digitizing tablets. As another example, a computer may receiveinput information through speech recognition or in other audibleformats.

Such computers may be interconnected by one or more networks in anysuitable form, including a local area network or a wide area network,such as an enterprise network, and intelligent network (IN) or theInternet. Such networks may be based on any suitable technology and mayoperate according to any suitable protocol and may include wirelessnetworks, wired networks or fiber optic networks.

Also, as described, some aspects may be embodied as one or more methods.The acts performed as part of the method may be ordered in any suitableway. Accordingly, embodiments may be constructed in which acts areperformed in an order different than illustrated, which may includeperforming some acts simultaneously, even though shown as sequentialacts in illustrative embodiments.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having,” “containing,” “involving,” andvariations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively.

What is claimed is:
 1. An apparatus for imaging a foot, the apparatuscomprising: at least one housing configured to accommodate a patient'sfoot, during magnetic resonance imaging; at least one radio frequencytransmit and/or receive coil; and at least one first releasable securingmechanism configured to engage with a member attached to a magneticresonance imaging system at a location such that, when the at least onefirst securing mechanism engages with the member, the apparatus ispositioned within an imaging region of the magnetic resonance imagingsystem.
 2. The apparatus of claim 1, wherein the at one first releasablesecuring mechanism comprises: a receptacle dimensioned to accommodatethe member; and a retention portion configured to resist movement of themember once the member has been positioned within the receptacle.
 3. Theapparatus of claim 2, wherein the retention portion comprises a firstarm portion and a second arm portion, each forming at least a portion ofthe receptacle, wherein the first arm portion comprises a firstprotrusion and the second arm portion comprises a second protrusion, andwherein the first protrusion and the second protrusion are configured toimpede the member from entering and exiting the receptacle, such thatforce on the first protrusion and the second protrusion is needed toallow the member to enter and exit the receptacle.
 4. The apparatus ofclaim 3, wherein the first protrusion and the second protrusion areconfigured such that a first force required to allow the member to enterthe receptacle is less than a second force required to allow the memberto exit the receptacle.
 5. The apparatus of claim 3, wherein the membercomprises a first portion having a first diameter and second portionhaving a second diameter less than the first diameter, and wherein thefirst arm portion and the second arm portion are configured to positionunder the first portion and to grip the second portion when theretention portion is engaged with the member.
 6. The apparatus of claim1, wherein the at least one first releasable securing mechanism allowsrotation of the apparatus about the member.
 7. The apparatus of claim 6,further comprising a second securing mechanism configured to preventrotation of the apparatus about the member when the second securingmechanism engages with the member.
 8. The apparatus of claim 7, whereinthe member comprises at least one recess, and wherein the secondsecuring mechanism is configured to fit within the at least one recessto prevent rotation of the apparatus about the member when the secondsecuring mechanism engages with the at least one recess.
 9. Theapparatus of claim 1, wherein the apparatus is tilted at an angle from avertical axis.
 10. The apparatus of claim 9, wherein a podal axis of theapparatus has an angle greater than 15 degrees and less than 75 degreesfrom the vertical axis in a direction of a longitudinal axis.
 11. Theapparatus of claim 10, wherein the podal axis of the apparatus has anangle greater than 30 degrees and less than 45 degrees from the verticalaxis in the direction of the longitudinal axis.
 12. The apparatus ofclaim 9, wherein a podal axis of the apparatus has an angle greater than5 degrees and less than 90 degrees from the vertical axis in a directionof a latitudinal axis.
 13. The apparatus of claim 12, wherein the podalaxis of the apparatus has an angle greater than 15 degrees and less than75 degrees from the vertical axis in the direction of the latitudinalaxis.
 14. The apparatus of claim 13, wherein the podal axis of theapparatus has an angle greater than 30 degrees and less than 45 degreesfrom the vertical axis in the direction of the latitudinal axis.
 15. Theapparatus of claim 1, wherein the at least one radio frequency transmitand/or receive coil comprises a plurality of receive coils.
 16. Theapparatus of claim 15, wherein at least one of the plurality of receivecoils at least partially overlaps at least one other of the plurality ofreceive coils.
 17. The apparatus of claim 15, wherein at least one ofthe plurality of receive coils is arranged above at least one other ofthe plurality of receive coils in a vertical direction.
 18. Theapparatus of claim 17, wherein the at least one of the plurality ofreceive coils arranged above the at least one other of the plurality ofreceive coils is offset in a horizontal direction from the at least oneother of the plurality of receive coils.
 19. An apparatus for couplingto a magnetic resonance imaging system for imaging a foot, the apparatuscomprising: at least one radio frequency transmit and/or receive coil;at least one housing configured to accommodate a patient's foot duringmagnetic resonance imaging; and a base attached to the at least onehousing, the base having a latitudinal axis and a vertical axisperpendicular to the latitudinal axis, wherein the at least one housingis tilted relative to the base along a podal axis.
 20. The apparatus ofclaim 19, wherein the podal axis of the apparatus has an angle greaterthan 15 degrees and less than 75 degrees from the vertical axis in adirection of a longitudinal axis.
 21. The apparatus of claim 20, whereinthe podal axis of the apparatus has an angle greater than 30 degrees andless than 45 degrees from the vertical axis in the direction of thelongitudinal axis.
 22. The apparatus of claim 19, wherein the podal axisof the apparatus has an angle greater than 5 degrees and less than 90degrees from the vertical axis in a direction of the latitudinal axis.23. The apparatus of claim 22, wherein the podal axis of the apparatushas an angle greater than 15 degrees and less than 75 degrees from thevertical axis in the direction of the latitudinal axis.
 24. Theapparatus of claim 23, wherein the podal axis of the apparatus has anangle greater than 30 degrees and less than 45 degrees from the verticalaxis in the direction of the latitudinal axis.
 25. The apparatus ofclaim 19, further comprising at least one first releasable securingmechanism configured to engage with a member attached to the magneticresonance imaging system at a location such that, when the at least onefirst releasable securing mechanism engages with the member, theapparatus is positioned within an imaging region of the magneticresonance imaging system.
 26. The apparatus of claim 25, wherein the atone first releasable securing mechanism comprises: a receptacledimensioned to accommodate the member; and a retention portionconfigured to resist movement of the member once the member has beenpositioned within the receptacle.
 27. The apparatus of claim 26, whereinthe retention portion comprises a first arm portion and a second armportion, each forming at least a portion of the receptacle, wherein thefirst arm portion comprises a first protrusion and the second armportion comprises a second protrusion, and wherein the first protrusionand the second protrusion are configured to impede the member fromentering and exit receptacle, such that force on the first protrusionand the second protrusion is needed to allow the member to enter andexit the receptacle.
 28. The apparatus of claim 27, wherein the firstprotrusion and the second protrusion are configured such that a firstforce required to allow the member to enter the receptacle is less thana second force required to allow the member to exit the receptacle. 29.The apparatus of claim 27, wherein the member comprises a first portionhaving a first diameter and second portion having a second diameter lessthan the first diameter, and wherein the first arm portion and thesecond arm portion are configured to position under the first portionand to grip the second portion when the retention portion is engagedwith the member.
 30. The apparatus of claim 25, wherein the at east onefirst releasable securing mechanism allows rotation of the apparatusabout the member.
 31. The apparatus of claim 30, further comprising asecond securing mechanism configured to prevent rotation of theapparatus about the member when the second securing mechanism engageswith the member.
 32. The apparatus of claim 31, wherein the membercomprises at, least one recess, and wherein the second securingmechanism is configured to fit within the at least one recess to preventrotation of the apparatus about the member when the second securingmechanism engages with the at least one recess.
 33. The apparatus ofclaim 19, wherein the at least one radio frequency transmit and/orreceive coil comprises a plurality of receive coils.
 34. The apparatusof claim 33, wherein at least one of the plurality of receive coils atleast partially overlaps with at least one other of the plurality ofreceive coils.
 35. The apparatus of claim 33, wherein at least one ofthe plurality of receive coils is arranged above at least one other ofthe plurality of receive coils in a vertical direction.
 36. Theapparatus of claim 35, wherein the at least one of the plurality ofreceive coils arranged above the at least one other of the plurality ofreceive coils is offset in a horizontal direction from the at least oneother of the plurality of receive coils.